Many public facilities built in Nazi Germany were areas of communal activity, embodying the core ideas on which the party was based on. The "Blut und Boden" (Blood and Soil) ideology sought to link German people back to their land by decreeing a perceived right by heritage, and is the origin of the Thing movement. A Thing is an term for the ancient gatherings of Norse and Germanic tribes in an outdoor setting, and in 1933 the Nazi Propaganda Ministry sought to tie these historic events with the German landscape and Nazi doctrine.
Outdoor areas called Thingstätte (or Thingplatz) were constructed on or near sites that had historical or mythical significance, and were made to look as natural as possible. Thingstätten were modeled from ancient Greek theaters to strengthen the link to the past and Nazism, and to even legitimize the Nazi view of history. People would gather here for "Völkisch" meetings to see theater performances and propaganda presentations. Over 1,200 Thing sites were planned throughout Germany, but only around 40 were constructed - the performances did not fare well with the people due to the harsh climate, and Hitler was not particularly impressed with the movement. After 1936, many Thing sites became areas for common folk festivals, outdoor plays, and musical performances.
The grounds of the Heidelberg Thingplatz cover 25 meters of sloping land, which is situated atop Heiligenberg (Holy Mountain), and overlooks the city of Heidelberg. The mountain is rife with ancient burial grounds, and at the summit was a Roman temple dedicated to the god Mercury. The location of this temple later became the site of Klosterkirche Saint Michael auf dem Heiligenberg (St. Michael Monastery, founded 1023). The Saint Michael Kloster became a ruin in the mid-1500s, and was excavated in the late 1800s.
The Thingplatz was constructed in 1934-1935 under architect H. Alker, who worked for the Reichsarbeitsdienst (Reich Labor Service). Two hexagonal towers were constructed for flags, lighting, and sound, and were considered a marvel of technology. On opening day, 20,000 people lined the 56 rows of seats to hear a speech by Joseph Goebbels. For a brief period it was used for Nazi propaganda plays, speeches, and entertainment until the radio became the more preferred medium to use for promoting Nazism due to inclement weather at Thingstätte sites, a broader listener base, and less expense in both time and money. Summer solstice festivals and other events took place here instead, and during WWII it was largely unused and soon fell into ruin. It has held festivals and events since the end of the war, and still remains as a public park to this day.
thirdreichruins.com has many great postcards of this Thingplatz, and others across the country.