Most historical towns have a concentration of monuments in one area (usually the center of town).  Prague is different: the "good stuff" is just about all over the city.  There is one focal point, however, in Prague: the Old Town Square.  This is where everyone meets, where everything starts.  

This wide open space is surrounded by points of interest: the amazing Gothic and Renaissance church of Our Lady Before Tyn, the memorial to Jan Huss, the Town Hall (with Town Hall Tower and famous Horologe), the Baroque Church of St. Nicholas, medieval buildings, Bohemian crystal shops, restaurants. 

The Prague Old Town Square is not only popular with tourists, it is also popular with thieves.  Many of them impersonate tourists (pretending to take photographs).  They operate in groups, with sophisticated cons, meant to distract and help you part with your wallet.  Not only the Old Town Square, but, unfortunately, the entire city of Prague is crawling with thieves, pickpockets, robbers and con artists.  Unfortunately, the Czech authorities have a "laissez-faire"  attitude, on the theory that thievery in Prague provides employment and increases the Czech GNP.  It almost looks like the police is getting a kickback!  If you plan to visit Prague, beware!