The Henninger Keller This is the largest cellar in the Burgberg. In 1884 it was enlarged to a tunnel which crossed the entire hill and reached its northern shaft after 861 metres. After Carl Linde's inventing of the cooling system (shortly after the cellar's completion), however, it was no longer needed as a storage for beer and was then (from 1916 on) used to grow mushroom cultures. In the last years of World War II the cellar was used as a scene for the operation ERNA. They wanted to build a bombproof military hospital and a production place for defence technology. Today guided tours are offered through the cellar from April to September every Sunday at 11 a.m. (meeting place Entla's Keller).