The cavehouse is very nice! It's small, but cozy. What we enjoyed the most was breakfast and dinner on the terrace with the wonderful view over the caldera. When we arrived, there were two bottles of wine, coffee and food for the first breakfast, which was very nice We cooked every night in the small kitchen, there is everthing you need to prepare a simple meal. We also recommend to do a kayaktour with Renas kayaks, that was great! Even at end of march was the water already warm enough to be in the water.
The apartement and its terrace is in the middle of three cavehouses, so you have to cross the terrace of your neighbour to reach yours and you are very close to the neighbours. But probably that is very common, if you want to stay in the heart of Oia.