Less than 20 minutes walk to the Temple of Zeus, 30 to the main hub of the city. The apt is absolutely fantastic, very chic and stylish. Yannis and Helene are very easy to contact and respond super quick. They have lots of fab tips of what to see and where to eat. The view of acropolis from the balcony is fab both in the morning and at night time when lit up.
For the city sightseeing:
There is a multi site ticket for the main sites including acopolis and Zeus, agora for only 30 euros - this lasts 5 days, acropolis alone is 20 euro. The sights of Athens tour bus (blue) is 16 euro compared to the other two in the city.