Helios cave house was the perfect place to stay for my short time in Santorini! I loved the layout of the space, as the kitchen and bathrooms are located outside the main area with the bedrooms and living room. This makes the home feel very spacious, and you end up spending so much time outdoors. With that being said, there is plenty of private space to enjoy a coffee, beer, or simply take in the lovely view :) Everything else about the house was perfectly clean and beautifully decorated. Another detail that made staying at Helios special is the fact that it is located in a very residential area. This added authenticity to being in Greece for the first time, as I felt it gave me a better sense for the culture. Lastly, it was easy to catch a bus from Mesaria (about 10 min walk down the road from Helios) to Fira. From there you can get to anywhere else on the island from the same bus terminal.
One word of caution - the bus to the airport from Fira runs only every 2 hours. So although I was able to get to Fira quickly on my last day, it didn't do me any good because the bus was leaving too late to get to the airport. So I ended up having to take a taxi (which would have been easier and closer if I had just done so from Mesaria). So make sure the timings match up for you!
Staying at Helios cave house was a great decision and I am sure you will feel so too!