The only problem with Sofia's place it was the fact I didn't want to leave.
The place is absolutely fantastic. It's perfect for one person, a couple or even for more people, if you are ok sleeping on the couch (which is very comfortable). I spent a whole month there, since I was working, I can say is perfect to rest, because the place itself is in a calm zone, but also close to many bars, coffee places, restaurants, and other services. Less than 10 min from 2 metro stations (line M3, which is directly connected to the airport). The place is fully equipped, with AC, TV, utilities and amenities, which is perfect for both short and long stays.
The best part is that the communication is easy and both Sofia and Nikkos are very friendly and helpful. If I ever go back to Athens, I'd definitely stay there again. It was one of the best Airbnb experiences I had.
Many thanks to both Sofia and Nikkos. I hope to see you again.