Hands down, the best place to get a covid test is the Athens airport. I suggest you take test when you land and before you arrive, as its likely that you're staying in the city and not near the airport (the airport is a bit of a drive from downtown Athens). There are antigen and PCR tests that allow for a day long window, meaning you don't need to arrive at a specific time to take the test. There is usually a bit of a wait but the process is smooth.
Street art is something that is super popular in Athens and is a beautiful reflection of the art and culture throughout Greek history. Greek street art exists all over the country and even on some islands but it is most present in Athens, where there is a vibrant and young student community. Here is a look at what some of the street art looks like, as you will see a lot of it is political and reflects many of the country's current issues.