Ortahisar (Turkish: Middle Castle), previously known by its Byzantine name Potamía (Greek: Ποταμία), is a town (belde) in the Ürgüp District, Nevşehir Province, Turkey.

In the early 1970s a young Scottish man named Craig Mair spent a year living in Ortahisar and wrote a book about his experiences called A Time in Turkey.

[4] Northeast of Ortahisar is a rock-cut monastery complex called Hallaç Manastırı which consists of a courtyard closed on three sides but open to the south.

The gathering of rubble over time means that the ground level is one and a half metres higher than it was when the structure was built, so the entrances to the monastic rooms are lower than the courtyard.

The tuff-stone local caves, with a constant temperature of 10 °C in summer and winter, are used to store citrus fruits, potatoes, apples and onions, some of it transported north from Mersin.