Prague's Old Town Square has two famous churches dating from different eras of Prague's history.
The first church is the Tyn Church (Kostel Panny Marie Pred Tynem--Church of Our Lady Before Tyn). The Tyn Church is a Hussite church dating from the early Gothic period of the 15th century. It is most recognizable with its spiked spires. The interior of the church is from the Baroque period.
I only saw the exterior of the church from the Old Town Square, but it is a beautiful sight to see and is the burial site of Danish astronomer Tycho Brahe, who was a consultant of Hapsburg Emperor Rudolf II. Brahe died in Prague in 1601 from a burst bladder. During the 15th and 16th centuries, the Tyn Church was a Hussite stronghold that the Hapsburgs were determined to destroy.
The other church that dominates the skyline of Prague's Old Town Square is the Catholic St. Nicholas Church (Kostel sv Mikulase), called a Baroque "wedding cake" by locals. This 18th-century church is located in the northwestern corner of Staromestske Namestie. St. Nicholas Church was built by Kilian Dientzenhofer, whose family was responsible for the design and construction of many other churches throughout Prague. This church is very tiny, but to me, it looked huge.
Author Franz Kafka was born next door to St. Nicholas Church at Celetna 3; this place is now a Kafka photo exhibit of his life.
So if you do the right thing and take the time to tour Prague, make sure that you take about an hour to see these two gems of Prague and its Old Town.