The Islam-aga Mosque is a small, well-preserved Ottoman mosque in the heart of Niš, standing near the central square on a site that was part of the old Turkish čaršija (bazaar district). It is the only working mosque left in the city and one of the few intact reminders of the three centuries of Ottoman rule that shaped Niš more than any other period of its history.
The building follows classic Ottoman design — a simple rectangular hall topped by a low dome, a slender minaret, a walled courtyard with a fountain. The interior is plain and functional; this is a working house of worship, not a tourist attraction, so visitors should dress appropriately and check whether they are welcome to look inside outside of prayer times.
The mosque sits in an interesting part of the city — you are very close to the old bazaar area and within easy walking distance of the fortress. It is easy to miss if you are not looking for it, which makes finding it feel like a small reward.