Main courtyard viewed from the Gate Tower. The Heidelberg Castle (Heidelberger Schloss) is one of Germany's most famous Renaissance and Gothic landmarks, perched on the northern slope of the Königstuhl hill overlooking the Neckar River and Heidelberg’s Old Town (Altstadt). First constructed around 1214, the complex evolved over several centuries into an impressive palace compound. Like many structures in Heidelberg, local red Neckar Valley sandstone was used in the castle construction.