I don’t know where the poster is getting information about underground newtworks at Göbekli Tepe. AFAIK there is no such evidence—at all. As to ancient sites underwater, that’s easy to explain: we’re on the tail end of an ice age and ocean levels have risen as ice melted.
i hadn't heard that either. It's close enough to Cappadocia though that there may be some confusion. There's also a conspiracy theory that the Turkish government is slow walking Gobekli Tepe for something very similar. Things were discovered that would upend our current view of history.