Castles, the River Mouth and the Floodplain Forest on the Lower Sakarya

Begin the day on the plain north of Adapazarı, at Harmantepe Castle. The Kültür Portalı writes that the castle is reached by a farm track branching left off the road from Küçük Söğütlü to Akçakamış village. According to the Provincial Directorate of Culture and Tourism, the last two kilometres of the road are unpaved but passable in every season; in rainy weather, it notes, access becomes somewhat harder. Leave the car at a wide spot on the track without blocking the passage of farm machinery.

First stop and look at the place where the castle sits. It stands on a small natural hillock in the middle of a flat plain. The Kültür Portalı explains that these surroundings were once wet and marshy, and were later turned into fertile fields by canals dug on either side. Picture the cultivated flatland you see today as a marsh; only then do you grasp how prominent a point the castle was in that setting. The Wikipedia article also reports that the castle was left in an exposed position in the middle of the wide plain and that a ditch is thought to have surrounded it, though its traces are unclear.

Know the visiting situation from the start. According to the directorate's page, cleaning and excavation work has been under way at the castle since 2023 and it is closed to visitors. So do not try to go inside; if there is a fence, tape or a warning sign, do not cross it, and do not step on the excavation area. The walls are easy to make out from a distance across the flat plain, so plan your visit as a walk around the outside.

As you walk around the line of the walls, read the plan. The sources say the castle has a rounded plan close to an ellipse; that is why you notice the flowing, cornerless line of the walls even from afar. The walls are 2 metres thick and between 8 and 10 metres high. Count the six towers, each about five metres by five, one by one, and look at the distances between them.

Look for two details on the towers. The first is the round holes: the directorate explains that wooden beams were laid in a grid inside the core of the towers to bind the fill, and when the beams rotted their places remained as holes. The second is the arrow slits facing in different directions at the top of the towers. The castle has five round arched entrances in different directions and of different sizes, the main gate on the south. Beside the gates there are said to be holes into which wooden bolts that locked the doors from inside were slid into the wall; look for them at the gateways you can see from outside.

A short note on the castle's date. The directorate and the Kültür Portalı date the building to the 12th or 13th century, while the municipality's tourism brochure dates it to the 12th century. Wikipedia reports that some researchers linked the castle to the canal project of the 6th century, but that the finds show it to be part of the chain of castles lined up west of the river against Turkish raids.

For photographs move to the south side of the plain; the face of the main gate looks this way and morning light strikes the walls from the side. With a telephoto frame the texture of the wall between the towers, the rubble stone and the lime mortar, reads well. The interior of the castle is covered with plants and trees, so in summer the top line of the wall can disappear into the green. Half an hour is enough here. As you leave, return from the farm track to the asphalt and head north-east towards Seyifler; the two castles are about 10 kilometres apart as the crow flies.

Source: Sakarya İl Kültür ve Turizm Müdürlüğü; Kültür Portalı; Sakarya Büyükşehir Belediyesi Turizm Broşürü 2025; Wikipedia.

Seyifler Castle is reached from the north of Ferizli, at the entrance of Seyifler village. The Kültür Portalı writes that the castle stands at the village entrance, 30 kilometres from the city centre. Do not expect a visitor centre or signposting here; the remains lie at the edge of the village, among trees and a covering of ivy. Leave the car at the side of the village road without blocking anyone's entrance and approach the remains on foot.

First look at the location, because that is the way to understand this castle. It was built on a peninsula-shaped piece of land at the point where the Sakarya River and the Çark Stream draw close and meet. Wikipedia reports that in antiquity this strategic spot was called Mesonesion, meaning Middle Island. The Çark Stream, according to the municipality's brochure, is a watercourse of about 45 kilometres that carries the overflow of Lake Sapanca and joins the Sakarya near Seyifler village. So on one side you have lake water and on the other the river; the castle holds a neck of land between the two.

The Kültür Portalı says the castle was most probably built on the road between the Black Sea and Adapazarı to secure the bridges over the Çark Stream and the Sakarya. It is a small castle of about eighty by eighty metres. Its date of construction is not known for certain; Wikipedia writes that it is thought to have been built in the 12th or 13th century, and the brochure also stresses that the date is uncertain.

Now look for what is still standing. The Kültür Portalı notes that the two semicircular towers in the western and northern parts are still on their feet. The brochure adds that these two towers stand about ten metres apart, with a stretch of wall surviving between them. Wikipedia explains that the remains stand by the stream, while in the field behind, now used for farming, the thick walls have largely collapsed and only their foundations remain. Do not walk into the fields; view the remaining walls from the roadside and from the stream side.

Pay attention to the section of the wall. The sources say the walls were built with an outer face of dressed facing stone and a core filled with rubble. At a collapsed corner you can see these two layers side by side; here you can read the inside of the masonry you viewed from outside at Harmantepe. Wikipedia also states that the building style of the two castles is the same.

Know what Wikipedia reports about this castle's place in history. According to the article, the castles of Seyifler and Harmantepe were seen as important for the conquest of the lands north of the river, Seyifler became the base of Orhan Gazi and was used in the campaigns towards the Black Sea coast. The Kültür Portalı, for its part, counts the castle among the frontier control towers lined up along the Sakarya, together with Harmantepe, Poyrazlar, Adliye, Kurtköy in Sapanca, Çobankale in the Geyve Gorge and the castles of Pamukova.

For photographs look for texture here. The thick wall covered in ivy shows stone and plant woven into one another in a close frame. Towards midday the shade of the trees lights the wall in patches, so an overcast day gives a more balanced picture. Half an hour is enough here. On leaving, continue north towards Karasu; the river mouth at Yenimahalle is about 22 kilometres away as the crow flies.

Source: Kültür Portalı; Sakarya Büyükşehir Belediyesi Turizm Broşürü 2025; Wikipedia.

When you enter Yenimahalle in Karasu you are very close to the point where the river reaches the sea. The Provincial Directorate of Culture and Tourism writes that the distance of about one kilometre from the entrance of the neighbourhood to the Black Sea has been paved with stone blocks and turned into a footpath. Leave the car at the entrance of the neighbourhood and walk this path from start to finish; spending the river's last kilometre on foot is the real point of this stop.

Before you start walking, think about where the river has come from. According to the directorate, the Sakarya rises in Eskişehir and, after travelling 824 kilometres, flows into the Black Sea within the boundaries of Yenimahalle. The Küre Encyclopaedia describes it as Turkey's third longest river after the Kızılırmak and the Euphrates, and the largest river of north-western Anatolia. The same source states that the river takes its name from Sangarius, the river god of Greek mythology. According to Küre, in the north of the Adapazarı Plain the river also takes in the Mudurnu Stream and the Çark Stream, which you just saw joining at Seyifler, before reaching the sea.

Along the way, watch the face of the river. The directorate also calls this the point where fresh water and salt water meet. You will see fishing boats moored on the bank and the centuries-old plane trees on either side of the footpath. According to the municipality's announcement, a walking and resting area, a cycle path, seating, shade structures and fishing spots were laid out over an area of 6,380 square metres; the municipality's brochure writes that this work was completed in the September 2025 season. It is a good place to sit on a bench and watch the river flow.

When you reach the sea at the end of the path, note the shape of the delta. According to the Wikipedia article on the Sakarya Delta, this delta does not form a marked bulge into the sea as the Kızılırmak and Yeşilırmak deltas do. Because the sea deepens abruptly and strong currents prevented such a bulge, the delta has developed mostly along an east to west line, parallel to the coast. The straight line of the shore you see when you look along the coast is the result.

The dunes on the shore are part of the same story. The article writes that the delta dunes, in the form of small hillocks, average five metres in height, and that this area counts as the longest uninterrupted dune habitat in Turkey. Do not walk on the dunes; the vegetation holds the sand in place and is easily damaged. Wikipedia reports that two plants endangered on a global scale, the Black Sea campion and the coastal mullein, live on these dunes.

The river mouth also matters as a habitat. The municipality's brochure notes that the Sakarya is famous for the sturgeon, whose caviar is highly prized. Wikipedia writes that efforts are being made to keep the endangered sturgeon alive in this mouth, and that the delta is a wintering area for the red-breasted goose and the velvet scoter. If you come in winter bring binoculars and watch the waterbirds along the shore.

The directorate says that swimming in the sea is also possible in summer; if you want to swim, pay attention to the waves and currents and do not enter the water where the river meets the sea. The municipality describes this as one of the finest places in the city to watch the sunset; after the last stop of the route you can come back here for the evening light. Spend an hour here, then set off west, parallel to the shore, towards the Acarlar floodplain forest.

Source: Sakarya İl Kültür ve Turizm Müdürlüğü; Sakarya Büyükşehir Belediyesi; Küre Ansiklopedisi; Wikipedia.

The last and longest stop of the day is the Acarlar floodplain forest. According to Wikipedia, it stretches between the districts of Karasu and Kaynarca, 6 kilometres west of the Sakarya River, surrounded by villages such as Denizköy, Karamüezzinler, Üçoluk, Taşlıgeçit and Camitepe. The Provincial Directorate of Culture and Tourism writes that access is by an asphalt road and that the area can be visited in every season. The site is run by the Sakarya Metropolitan Municipality and entry is charged; check the municipality's current announcements for the fee and hours.

Before going in, know what a longoz is. A longoz is a floodplain forest that is under water depending on the season. According to the directorate, the area covers 1,562 hectares and is a first degree natural protected site. Wikipedia describes it as the largest single-piece floodplain forest in Turkey, giving its length as 7.5 kilometres and its width as between 250 and 1,250 metres; the municipality's brochure uses the same description. The ministry's promotion platform Go Türkiye, however, calls it the country's second largest floodplain forest after the İğneada Longoz; the difference between the two descriptions may come from the single-piece criterion.

Set out on the footpath. The directorate notes that there is a footpath with a total length of one and a half kilometres, which visitors can walk comfortably, and viewing piers. Walk the path without hurrying and stop for a few minutes at each pier; that is why we allow two hours for this stop. When you look at the water from the piers you will see tree trunks rising straight out of the water, the image that sets a longoz apart from an ordinary forest.

Try to identify the trees. The directorate writes that the forest is entirely surrounded by ash woods and that these trees push into the marshy parts of the lake in places. Wikipedia adds that alder, beech and elm species are also common in the forest besides ash. On the surface of the water look at the water lilies; the Kültür Portalı states that the forest is home to around 2,300 plant species, among them the water violet, the summer snowflake and water lilies of various colours. Wikipedia reports that in Turkey the water violet is found only at Acarlar. The municipality's brochure says that the area takes on its liveliest appearance in the spring months, when the endemic plants appear.

Remember that the water changes with the seasons. According to the directorate, the longoz dries out in the summer months and forms again in winter as water collects, reaching a depth of up to one and a half metres. It is also noted that the land from which the water withdraws in summer is used by villagers as farmland. So the view you find will differ a great deal depending on the month you come.

Keep quiet for the birds. Go Türkiye writes that the forest is home to 243 bird species. The Kültür Portalı states that pheasant, woodcock and wild duck live here. Wikipedia reports that the area lies on one of the two important migration routes crossing Anatolia and that species such as herons, cormorants and wild ducks stop over here. If you have binoculars use them on the piers, and do not talk loudly.

You can also understand how the longoz formed by looking towards the shore. Wikipedia describes the area as a typical coastal barrier lake: the streams flowing to the sea were blocked by dunes, and the hollow behind the dune barriers filled with water. The dunes separating the forest from the sea are 20 to 25 metres high. You are on the inland side of the dune belt you just saw at the river mouth.

The Kültür Portalı notes that boat and pedal boat trips are run in the forest; Wikipedia, on the other hand, records that touring with motor boats during the nesting season harms the waterbirds. So if you want to go out on the water, choose a rowing or quiet option. Put on insect repellent, keep to the footpath and take your rubbish back with you. If there is still time before sunset at the end of the two hours, you can return to the river mouth at Yenimahalle and close the day there.

Source: Sakarya İl Kültür ve Turizm Müdürlüğü; Kültür Portalı; Türkiye'ye Git; Sakarya Büyükşehir Belediyesi Turizm Broşürü 2025; Wikipedia.