Can't say I enjoyed it. Coming back to Europe reminded me why I hate hot weather. The city itself looks run down, it feels like walking around bad neighborhoods of other cities. Of course I accidentally booked an apartment in the red light district so probably had to deal with shitty streets and junkies on a much higher frequency, but even the city center does not look much better. People seam friendly and ready to help/talk which is not easy to do when you can't understand a word they are saying. A lot of people smoke and they do that even indoors so you can't even go inside a pharmacy without breathing that crap in. I might someday return to Greece to check some islands or something, but as for the Athens I had enough. Also maybe it's a different view after traveling Asia, but the prices are not that low.
The currency is Euros (EUR).
You can't get a local SIM card at the airport (it feels like middle ages), there was some comments that you could get it at post office, but they are mostly ended with "it won't work in any case". I got one from some small shop (Cosmote card), 6 GB for 6 €. Not sure if it was the problem with the card or if it's the network in general, but data speeds are bad (at best could get 3G and that not always).
There is some restaurants and taverns around. I tried some Greek dishes, but did not really like them and the prices are steep. Not the fan of all the gyros so mostly just kept making food at the apartment.
National Garden a decent sized park in the city. Very nice in the hot weather as it has lots of shadows to hide in.
Traffic / Walking
Walking around is not very pleasant. Even in the city center it can feel unsafe (with people making drug deals and just looking fishy), the streets are covered with poop and urine, and in the Summer it's so hot. I did like finding some interesting graffiti.
Uber is kind of available. You can use the app, but it will call a normal taxi. Still better than having to use just-another-app as you get the ratings and your account is charged for the ride.
To get from/to airport is 38 €.
Entertainment / Visit
National Historical Museum a national museum, easy to navigate and has some interesting exhibits. Price is 3€.
There is all those Akropolis and similar ancient places, but at best I found them "meh". It's just too hot to be exploring them and it's still most of the time just a pile of boring rocks. If you do want to see them you can get a multi-place ticket for 30 € (get somewhere where is less people and you won't need to stand in line).
(from external source) Spring and late autumn are the best times to visit. Summer can be extremely hot and dry during heat waves (rarely happens). Winter is low season with occasional rainy or snowy day.
I was visiting beginning of June, it was very hot and dry.
For other locations in the world see intro article.