The Heiliggeistkirche is Heidelberg's largest and most important church, located in the heart of the Marktplatz. Built between 1398 and 1515 in Gothic style, it originally served as the burial place of the Electors Palatine and housed the famous Bibliotheca Palatina, then Germany's largest book collection. Today the church receives 1-3 million visitors annually. The church tower with its 204 steps offers the most stunning panoramic views of the Old Town, Neckar River, and castle. Regular organ concerts are held on Fridays and Sundays.