We had a lovely stay at Gravitate in late September 2014. However we did not meet our host until the day before we left. When we finally met she did call a taxi for us for the following day and arranged for a porter (we paid him) to carry our luggage up the 80 steps to catch the taxi.
The views of the Caldera are amazing and there is plenty of room on the veranda to sit out and watch the sun set. Elvira left clear instructions about the WiFi, turning on the water heater before each shower, offering food recommendations, and details about NOT flushing toilet paper. We were a group of four women and managed well with one bathroom and three beds. We would have appreciated a set of clean towels during our four-night stay. The rental has no windows--see description of cave--but the place is clean, near the public bus stop and a short walk to Fira. Carefully read about the many steps required to access the rental or get back to the shops in Firastafani. We had a lovely time in Santorini!