Ortahisar (Turkish: Middle Castle), previously known by its Byzantine name Potamía (Greek: Ποταμία), is a town (belde) in the Ürgüp District, Nevşehir Province, Turkey. Its population is 3,086 (2022). Ortahisar is located about 20 km east of the provincial capital, Nevşehir.

Until the mid-2010s Ortahisar was rather off-the-beaten-track when it came to Cappadocian tourism. It is now much better known and many boutique hotels have been created out of its fine old stone houses.

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.