From the Wikipedia: Kanlıdivane (ancient Canytelis) is an ancient city situated around a big sinkhole in the Mersin Province. It was part of the Olba kingdom. In the northern necropolis, there is a mausoleum, which was built by the Queen Aba for her husband and sons. On the inscription of the tower at south-west it reads; "Built by Teukros, the son of priest king Tarkyaris of Olba for Zeus." By the first century, Olba kingdom became a part of Roman Empire. Byzantine Emperor Theodosius II rebuilt the city as a Christian religious center and renamed it Neapolis. There are ruins of basilicas, cisterns, rock cut graves etc. around the sinkhole. Kanlıdivane means "bloody crazy". This may refer to the red color of the surrounding soil. The name may also refer to a dreadful legend according to which the criminals had been executed by throwing them into the sinkhole during Roman times [elsewhere I read bloodthirsty animals roamed that hole, to make matters worse or just clean up the mess].

Most of the building remains are from the 8th and 9th century, amongst them four churches with the same groundplan: basilal, with three naves). Every year during the Mersin International Music Festival one or two outdoor concerts are held in Kanlıdivane. The audiences and performers sit at the opposite sides of the sinkhole. (During such concerts Metropolitan municipality of Mersin supply free bus trips to Kanlıdivane.)

In 2015 I went here again. Obviously things were being prepared for a bigger stream of visitors, a parking space was under construction, and some kind of path along the sights was being laid out. I hope it will remain possible to just wander around.

I grouped some of the most obvious sights into sub-galleries, the main gallery has many pictures of the sinkhole, followed by pictures taken randomly while walking the area. They mostly go without captions.

Note that maybe 500 meters down the road there are the Çanakçı rock tombs. On the map indicated as 12.