Costa's place is in a perfect location - just a few steps from the park that hosts some of the most renowned ruins Athens has. At first, we were surprised it was a semi-basement, but then we realised it was an advantage for us - the rooms were rather chilly, despite the extreme heat outside the house. The only inconvenience was the mouldy smell you could feel when the heat was too unbearable.
Costa is extremely kind and answers any question you might have. All in all, this place, with its pluses and minuses, is an absolute great deal and I would rent it again.
If you don't feel like making your own coffee, in 2 minutes you will get to The Underdog - a speciality coffee place with amazing brunch food and delicious coffee. 3 more minutes and you get to the crowded streets of the old town - beware of the tourist traps some restaurants hide: prices per 100 grams instead of portion are easy to spot if you pay attention. If a waiter insists you enter their terrace, they most likely have mediocre food, at best.
I cannot state enough: have dinner at Kuzina. With several mentions in the Michelin Guide, it has amazing food, rather large portions and well educated staff. Also, it's the place were I realised Greece can also offer great wines.
An Uber trip to the beaches can cost between 8 and 20 euros, depending on your choice. I recommend Voe Beach Bar - they let you use their sunbeds for free and sell nice cocktails for decent prices.
PS: If you feel like exploring, go to Aegina Island - they are famous for the pistachio and the beaches are uber cute.