The Fethija Mosque is Bihać's oldest surviving building and one of the most architecturally interesting in the town. Originally a fifteenth-century Gothic church, it was converted to a mosque after the Ottoman conquest in 1592 and has remained one ever since, its double identity still visible in the hybrid architecture.
The building stands near the river in the old town, close to the Captain's Tower. The interior is modest, but the exterior shows the Gothic ribbed vaulting and pointed windows of its original construction alongside the later Ottoman elements. Non-Muslims are generally welcome to look inside outside prayer times. There is no formal admission charge, though a small donation is appreciated.