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Photo: BishkekRocks, CC BY-SA 3.0 via Wikimedia Commons
The Heiligenberg mountain, north of the river, boasts a wonderful view over the old town. Also on the Heiligenberg are the remnants of a wall ancient Celts built to keep Germanic tribes out, the Heidenloch, a deep well with unknown origins, and the ruins of the 10th-century cloister St. Michael.
The Heiligenberg is a large wooded hill overlooking the town of Heidelberg in Baden-Württemberg, Germany. It rises to around 440 metres NHN. It has been the site of many historic and pre-historic constructions, including a Celtic hilltop fortification, a Roman sacred precinct, several medieval monasteries, modern lookout towers and the Heidelberg Thingstätte, built by the Nazis in the 1930s.
© OpenStreetMap contributors
The Thingstätte on top of Heiligenberg (an open-air theatre built by the Nazi regime in 1934 to host propaganda events)
Street on the northern side of the city. It provides a wonderful view across the oldest part of the city. Here you can find the site of the famous Merian Stich, an engraving that is a popular illustration of Heidelberg.
Old Bridge, Alte Brücke
Bridge constructed in 1788.
The old armoury is now a student cafeteria (open to the public and offering good food and drinks at reasonable prices).
The Heiliggeistkirche (Church of the Holy Spirit) is only one of many large and small churches, but definitely the one with the most interesting history. During the Dark Ages, it was the shelter of the Bibliotheca Palatina, Germany's oldest library. The Bibliotheca was stolen and brought to Rome but eventually returned in pieces. Today, parts of it can be visited in the University Library (also the oldest and probably the most valuable of its kind in Germany), which is situated close to the old university. You can get a great view of the Heiliggeistkirche, Old Town, and the Neckar river bridge from the castle (Schloss Heidelberg).
Hauptstraße is the main street, which leads from Bismarckplatz across the old town. Approximately 1.6 km in length, it is reputedly the longest pedestrian shopping street in Germany.