This is the Kurşunlu ("with lead" - on the roof) Mosque. It dates back to 1525 and is the heart of a group of buildings, some of which - two caravanserais - are by Sinan, the famous architect. In 2006 much of it was closed, and the mosque itself was due to be restored. The complex as a whole is well worth a visit, as is the surrounding neighbourhood with old houses.