Had a wonderful stay in a private real cave! My friend and I stayed during off season, October 2016, and still enjoyed the cooler days in Fira, Santorini.
Check in does not start any earlier than 3pm, and check out is at 11am. Reception was helpful when I had trouble returning my ATV one morning. Him and another guest offered to follow me to Oia and take me back to Fira. I was grateful for that.
Breakfast was okay, I think there could be more fresh fruits and maybe host nightly events to bring guests together (like beer night or game night).