We had an amazing time staying at Penny's place. The location is a short 10 minute walk to the acropolis and plaka areas. There was a grocery store just a few meters away with lots of options (even for vegetarians!). And the apartment itself is absolutely beautiful -- very thoughtfully arranged and very modern. Everything was extremely clean. We took a taxi from the port for about 20 euros.
Would highly recommend, and would definitely stay again next time we are visiting Athens.