My friend and I stayed at the Gemini Cave for two nights and had an absolutely amazing time. The photos don't do it justice - it's a truly beautiful place with a great view from the spa! It's a bit outside of Oia town, but an easy 15 minute walk and the bus is close by too. Natasa and her brother Stefanos were wonderful hosts and very happy to help if we had any questions. Would highly recommend staying here!
Also - an excellent restaurant just opened the day we arrived in Finikia, a 3 minute walk from the property - Lefkes - so if you do stay here make sure to go there! The best food we had in Greece.