Athens is a summer habit to attend open cinemas, that are seasonally open. There are so many and offer different kind of options, and of course they are everywhere in Athens. Here is a list according to location, starting where else but from Plaka.
Athens historical center (Plaka- Thisseio- Syntagma)
Not far from Plaka, but you have to walk towards either Thisseio via Adrianou street, or Pnyx hill via Areopagitou street, you can reach cine Thisseio.
Thisseio- Cine Thisseio http://cine-thisio.gr/
If you want to go to Syntagma, there is one more open air space for movies, inside Zappeion and National Garden. That is Aigli, where you can have also dinner or drink later.
Syntagma- cine aigli http://www.aeglizappiou.gr/cine_uk.html
If you want to leave Syntagma and walk towards the other hill, that of Lycabettus (or better take a taxi there, you can go to Kolonaki cinema, Dexameni Square Cinema.
Kolonaki – cine dexameni https://cinedexameni.gr/
Near Filopappou hill the cinema you can find is Zefiros, Troon 36, Petralona.
In case you do not want something that cosmopolitan, you can move to Exarhia and approach Riviera.
Exarhia –Riviera cinema, Valtetsiou 46
And more options around Athens
Filothei Cinema, Platia Drosopoulou, Filothei Psichiko 152 37 (close to Athens centre, and you can easily get there by a taxi).
If you want to move even norther to Kifisia, famous location is Mpomponiera cinema, Papadiamanti 12, Kifisia 145 62. In the opposite direction, at the south of Athens, you can visit cine Arian, located at Glyfada, Metaxa avenue 11, 16675.
Please keep in mind that the above options are for SUMMER only, since during autumn and winter open air cinemas are closed. Hope you enjoy your night!