Camden catacombs

From the Wikipedia page

The Camden Catacombs are a system of underground passages in Camden Town underneath part of the Camden markets, constructed in the 19th century, as of 2012 owned by Network Rail. They are not true catacombs (repositories for dead bodies), but an underground area originally used as stables for horses and pit ponies working on the railways. The catacombs also included an underground pool for canal boats operating on the nearby Regent's Canal. Not open to visitors due to danger of flooding