Heidelberg is one of the few larger German cities that has a significantly large 
preserved old part. This is due to the reason that during the Second World War Heidelberg was not affected by the bombing of the Allied troops. One of the alleged reasons was its popularity, which was written about by writers and philosophers such as Mark Twain, 
Ernest Hemingway, Hegel, Wolfgang Goethe, Friedrich Hölderlin, Karl Jaspers, and others. Due to this popularity, as well as to its strategic location, the decision of the American military forces to choose Heidelberg as their post-war center in Europe is also due. At 1.6 km, one of the longest pedestrian areas in Europe is located in the old part of the city. Many of the sights, museums, as well as numerous shops, cafes and bars are located on it. Much of the architecture of the old town is marked by the preserved Baroque architecture.
Among the more famous sights are:

The old part of the city, with many historical buildings

Rupprecht-Karls University
The student cell
The Path of the Philosophers
The Christmas market
Print-Media-Academies
The Cathedral "St. Spirit' 
(built in several stages over centuries and marked mainly by the Gothic)
The Jesuit Church (completed in 1759)
The church "St. Peter" (the oldest in the city, built in the 12th century) and others.