We were there by suggestion of a friend...definitely not the best place to stay at in Santorini.
Breakfast (an awful one) is charged 5 euros, whilst you can just cross the road and have a nice breakfast at the bakery open 24h a day (friendly staff and speaking lots of languages, from Italian to English, and French as well).
Better avoiding it, if you can.

Me and my girlfriend stayedat petra nera hotel on july!Mr giannis meet us at the port and took us to the hotel.our room was great ,with tv air condition ,clean.they provided us with clean towels every single day!theese are the things that you need on vacation in my opinion plus the smile and the help from the staff...Great job petra nera bravo!Sas euxaristoume polu gia ola!See you again next year!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

My girlfriend and I stayed at Petra Nera for a week earlier this month and found the hotel to be not only beautiful, but also highly economic. Service was great and the hotel owner, Yiannis, even picked us up from the ferry port. I would definitely recommend Petra Nera.

Petra Nera Hotel was a little far from the city and the buses did not pass very frequently, but the personnel of the hotel were very helpful and thoughtful. Our room was very comfortable and a good size for 4 people. The hotel is close to the black beach, which is a beautiful beach by the way, therefore it was nice to just go to the beach and walk back to the hotel. The facilities are very clean and the price was very appropriate. I speak for the four girls with whom I travelled, we would refer this place to anyone. We loved it!