The Büyük Ağa Medresesi (Great Ağa Seminary) is a late Ottoman theological school built in 1488 on the orders of Hüseyin Ağa, the chief white eunuch of the imperial harem. It stands slightly apart from the compact historical centre, on the north bank of the river toward the eastern end of the old town. The octagonal plan is unusual for a medrese and gives it a distinctive silhouette.
The medrese was still functioning as a religious school until the 20th century and has been carefully maintained. The courtyard and facade show the characteristic refinement of late 15th-century Ottoman craftsmanship — fine stone carving, elegant proportions, and a sense of repose that is easy to appreciate if you arrive without a busload of other visitors. It is often quieter than the more famous sights closer to the centre.