Thanks to Aris, we had two enjoyable days in Athens.
The flat is very central and very close to the metro station. There are cafes, bars and supermarkets around. The neighbourhood is very nice and safe. Note that, the entrance of the building is just across the gas station (i guess it was BP), we had a tiny problem with finding but it was solved quickly.
It was just for two people, neither bigger nor smaller. There were everything one can need. Kitchen, bathroom, bedroom were all well equiped.
I would definitely stay here again when I come back to Athens. Totally recommended.