Windmill bellavista is outstanding! We stayed for 5 days an would not hesitate to come back again...
Margarita was an exceptional host. She organise transport to and from the port, and got us a great deal on a moped. Could not ask for more.
The room was better than expected with a breathtaking view. This is fantastic value and the best location for seeing all of sifnos.
Public transport is within walking distance as are the towns of artemonas and Apollonia, but I recommend a vehicle.
Also look into booking directly through their website as breakfast is included in that case, but not with airbnb.