Perfect location with tons of room to spread out! Konstantino's place is within easy walking distance of plenty of great bars and restaurants, as well as a metro stop with direct access to the airport. While the surrounding neighborhood is vibrant, the apartment itself is tucked away on a quiet street, so you shouldn't have any noise-related problems sleeping. And if you still can't sleep, there's no better place to spend time than on his lovely balcony with a glass of wine.
Depending on your mobility and inclination, the apartment is walkable to all the major sites -- though some are obviously closer than others. I had no trouble walking as far as the Panhelenic Stadium and Mount Lycabettus, though they may be a bit too far in the hot summer months.
Would absolutely stay again.