A beautiful and a very clean house close to Apollonia. We were a group of 6 and the house suited exactly our needs. Our host was extremely kind and helpful with everything we needed and made us feel like home. The only downside (and this is aimed towards people who don't like walking) the house is a bit far from Apollonia (a 10 minute walk on foot), but still there are 2 bus stops really close to the house, so you can take the bus to go anywhere you like (they come and go really often, so you don't have to wait too long).
We totally recommend Καίτη's place for anyone who wants to see Sifnos, wants peace and quiet and to be near to all the events that take place in the island.