The large sandstone hill on which the city's castle was built is riddled with cellars and passageways, which have been used for a number of purposes over the centuries. The first recorded use dates from 1380 when a vault was used as a small brewery and a place to store beer. Among its other uses the Felsengänge (literally 'rock hallways') is as a natural place for storing water. Rainwater percolates through the rock and the resulting 'suspended' water tables once provided safe, clean water for the population of the old town below. During WWI, the vaults also provided safety for the city's population during heavy bombing, and was also used as a place to keep Nuremberg's numerous art treasures.