The square had not always been a square. At the centre of the today square and in front of the mosque, there was military infrastructure. Moreover, Hadrian’s Library was not just the wall that you can see today, but a building that was burned during the Great Fire of 1884. It was the time when Elgin’s clock was burned near Old Agora Square (you can see it in the photo).
The square is one of the main Athens points, and actually is the limit of Plaka to the south, connecting the Acropolis with Keramikos, and next to Psirri area. There is a metro station, quite central, two amazing historical buildings, plenty options for street food but also the start of two markets:
The two historical buildings are the Pantanassa church, a historic landmark of Athens, a previous monastery that gave its name to the area name coming from <monastery. Also, the mosque that survived Ottoman period, is one of the most important places to visit in Athens.
There are also some street food spots just outside the metro, where you can enjoy fresh fruits. Also some top night bars that offer magnificent view to Acropolis hill are located around the square.
From Monastiraki you can walk down Adrianou street and get to Thisseio- where there is a metro station as well-, where is a bus station for western Athens suburbs.