A Hellenistic tower stands almost at the edge of the sinkhole. It is quite a landmark, and I gave it a gallery by itself (though it may appear in other pictures).
The Wikipedia mentions there is an inscription: "Built by Teukros, the son of priest king Tarkyaris of Olba for Zeus."
It has no number but is close to number 9 on the map (which is the circular space at the entrance).