Dates back to at least the 5th century BC. Significant sections of city walls are still extant. Some of the ruins are underwater, though unlike at the Kekova sunken city (offshore at Kaleköy), you are still allowed to swim among these ruins. It is not very deep in most places, so even without snorkelling gear you can still get good views.

Because this location is so isolated, this is very much an ‘off-the-beaten-path’ site, making exploration of it (especially the underwater portions) that much more interesting. Snorkelling gear can be borrowed from the nearby Purple House.

The linked Wikipedia article has some good background info on the site. Also linked is an article on the histolia.de site – the article is in German but is readable using Google Translate. Also, that site has a layout map of the site which might be handy.