Old Town Square is located in the very heart of Prague and it is the most renowned square in the city. This place can get quite busy, especially in front of the famous Astronomical Clock. There are also other interesting historical sights to be seen, for instance the beautiful building of Kinsky Palace or Saint Nicolas church.
Take a walk through the historical part of the city, have coffee in one of the cafés nearby, buy souvenirs in gift shops or just enjoy its unique atmosphere. But be aware that due to the square's popularity, things often get quite overpriced here.
Wikipedia https://en.wikipedia.org/wiki/Old_Town_Square
Address 14 Staroměstské náměstí, Praha 11000, Czech Republic
Coordinates 50°5'14.806" N 14°25'15.398" E