Hinterbrühl (German pronunciation: [ˈhintɐˌbʁyːl] ⓘ) is a town in the district of Mödling in the Austrian state of Lower Austria.

The prisoners there built parts, sub-assemblies and BMW 003 turbojet engines for the He 162 Spatz (sparrow) jet fighter in a hastily converted underground factory during late autumn and spring 1945.

Hinterbrühl was just part of a vast crash production program where dozens of factories of varying sizes would make parts for the jet, then send them to sites like Hinterbrühl for final assembly and transshipment to flight test centers — or even directly to airbases, such was the desperate last-minute nature of the enterprise.

In 1912 a blast released millions of gallons of water and flooded the lower caverns of the mine, creating the largest underground lake in Europe.

In the 1930s a team of cave explorers found the lake and finally managed to open the grotto for the public.

The upper (non-flooded) tunnels of the same old mine were reused by Nazi German authorities as an aircraft-manufacturing facility which used forced labor.