Bolu Province in the context of "Zonguldak Province"

Bilecik Province (Turkish: Bilecik ili) is a province in midwest Turkey, neighboring Bursa to the west, Kocaeli and Sakarya to the north, Bolu to the east, Eskişehir to the southeast and Kütahya to the south. Its area is 4,179 km, and its population is 228,673 (2022). Most of the province laid down in Marmara region but eastern parts of Gölpazarı and Söğüt district and districts of İnhisar and Yenipazar remained in Black Sea Region, smaller southeastern parts of Bozüyük and Söğüt remained in Central Anatolia Region and smaller southwestern part of Bozüyük remained in Aegean Region.

Eskişehir Province (Turkish: Eskişehir ili) is a province and metropolitan municipality in northwestern Turkey. Its area is 13,960 km, and its population is 906,617 (2022). Its adjacent provinces are Bilecik to the northwest, Kütahya to the west, Afyon to the southwest, Konya to the south, Ankara to the east, and Bolu to the north. The provincial capital is Eskişehir. Most of the province is laid down in Central Anatolia Region. Northern parts of Mihalıççık district and ones of Mihalgazi and Sarıcakaya are located in the Black Sea Region and one of them belong to the Aegean Region.

Eskişehir is an old and culturally developed province of Turkey. Eskişehir has 3 universities, Eskişehir Osmangazi University, Eskişehir Technical University and Anadolu University, which is the largest university in Turkey and which has some branch offices in Europe.

Sakarya (Turkish: Sakarya ili) is a province and metropolitan municipality in Turkey, located on the coast of the Black Sea. Its area is 4,824 km (1,863 sq mi), and its population is 1,110,735 (2024). The Sakarya River creates a webbing of estuaries in the province, which is in the Marmara Region. The adjacent provinces are Kocaeli to the west, Bilecik to the south, Bolu to the southeast and Düzce to the east. The capital of Sakarya is Adapazarı. Its climate is maritime in the north and humid subtropical in the south and changes by the distance to the Black Sea.Sakarya is on the Ankara-Istanbul highway and is also connected by rail. Sakarya is serviced by Istanbul's Sabiha Gökçen International Airport. The mayor of Sakarya is Yusuf Alemdar as of 2024 (AKP). The city of Sakarya, one of the most important cities in Turkey for its rapid growth and development, is known for its natural surroundings and culture. Home to several resort towns, Sakarya has access to the sea, beaches, lakes, rivers, highlands, thermal springs, traditional Ottoman lifestyle districts such as Taraklı and Geyve and noteworthy historical relics from the Byzantine and the Ottoman eras.The Turks conquered the city of Sakarya in the 13th century. There was intensive immigration from the Caucasus and the Balkans in the 18th and the 19th centuries. The last massive immigration was in 1989 from Bulgaria. The pronvince's location at a transportation crossroads has made spurred development in the manufacturing sector, and it still has inward migration from other parts of Turkey.

Düzce Province (Turkish: Düzce ili) is a province in northwestern Turkey. The province is on the coastline of the Black Sea and is traversed by the main highway between Istanbul and Ankara. The primary town is Düzce, located in the center of the province. There are ancient Greek ruins in the province. Düzce separated from the Bolu province and became a province in its own right after a devastating earthquake in the city in November 1999. Its area is 2,492 km, and its population is 405,131 (2022).

Bolu is a city in northern Turkey, and administrative center of the Bolu Province and of Bolu District, located on the highway between Istanbul and Ankara. Its population is 184,682 (2021).

The city has been governed by mayor Tanju Özcan (CHP) since local elections in 2019. It was the site of Ancient Claudiopolis and has also been called Eskihisar ("old fortress") (and as such has several Turkish namesakes).