It was our first time in Greece and we went to the apartment by metro (what was about 5 minutes walking distance). Dimitris waited for us and explained us everything. He was very friendly and helpful. The apartment is nice and clean and well located. If you walk to the centre it takes about 30 minutes but the taxis are very cheap. We paid between €4 - €6 to get to the city centre. Just pay attention with taxis you take in the centre itself, some drivers try to give you a 'special' price on forehand that is three times as high. Always ask the driver to turn on the taximeter, then it will be fine.
There is a bakery next to the apartment, a big supermarket across the street and there are several restaurants nearby where we tried delicious Greek food.
I really loved my stay in Athens and would recommend this apartment to everyone!