The village of Güzelsu lies beneath the Hosap Kalesi about 60km/37mi southeast of Van on the way to Baskale. It was built in 1643 by the local Kurdish prince Sari Süleyman on the ruins of its 14th century Seljuk predecessor. The massive construction on and around a steep-sided rock was used in antiquity as a watchtower to survey the military
road from Van along the Cuh pass to northern Persia.
The complex of several storys contains three baths, two mosques, a medrese, a well, cisterns, prison and 360 rooms spread over several floors - all of which can be reached by passing through an impressive entrance hall with inscriptions and a lion relief and mounting some steep steps. The citadel which is itself surrounded by huge stone walls is reinforced by a town wall with equally thick walls and four towers. The wall surrounded the town of Hosap to the north, where today some of the houses are made from sun-dried bricks. A Kurdish-Ottoman bridge over the Hosap Suyu links the castle to the old military road, which at this point passes through a narrow gap in the rock. The Kurdish fortress Mahmudiye Kalesi takes its name from the local dynasty.