We really enjoyed our stay at the hideaway cave!
We were greeted by Maria's staff at the post office. The cave can only be accessed via the pedestrian walkway and some steep stairs; thankfully there was a porter available to carry our suitcases as it would have been a challenging journey otherwise. The staff provided us with recommendations of things to see and do in the area.
The cave was very nice! Two bedrooms with decent beds, air conditioning in the main area, a couch and a small table with some chairs. It was surprisingly quiet at night for being so central. There's a patio out front with a table/chairs and umbrella. You can see the sunrise from the patio and it's in a great spot to get out in Oia early in the day before the crowds.
The one caution: if you have any accessibility concerns, this is not the place for you. To reach the cave you have to go down several sets of steep, uneven stairs without railings. This was not a problem for us but it definitely meant we didn't have drinks if we were going home after dark.
On the plus side, being down several flights of steps off the main pedestrian path meant it was a bit quieter and less busy than the central areas.
Cleaners came everyday while we were out, and we were able to store our bags in a different location for a few hours after checkout.
Overall would recommend if you are looking for a reasonably priced, centrally located spot in Oia!