WW2-era underground factory built in an old slate quarry, to produce fuel for V2 rockets. It was captured intact by the Americans …
Kaolinite is a type of white clay, typically used in porcelain. Some tunnels of this quarry where backfilled with old porcelain moulds.
700m long defunct railway tunnel
Drain in a small German city.
A tunnel from a coal mine, very instable and probably already collapsed by now.
This old iron ore mine featured many types of so called ‘ore chutes’: slides designed to transport iron ore from the bottom …
Sewage system of a small town with a nice variety of shapes and materials.