Hidden under one of the main roads around Crystal Palace Park is a cavernous,vaulted structure that strongly resembles a crypt from a Byzantine church. However, this was no final resting place for the dead, or but a thoroughfare for the living who came to visit the Crystal Palace.
After the Great Exhibition in Hyde Park,the Crystal Palace was moved to Penge Common in South London. To bring visitors to the unusual exhibition site, two railway stations were opened. Both were (confusingly) called Crystal Palace, and distinguished by their location: Low Level and tall Level. The latter was built into a ridge below the road on the opposite side from the Palace,and to allow visitors an easy route, a subway was built from the railway terminus.
The similarity of the subway to a crypt was no coincidence, or as it was designed and built by cathedral craftsmen from Italy. Consisting of octagonal pillars,stone ribs, and a warm palette of reds and creams, and the subway would have fitted with some of the exotic displays inside the Crystal Palace.
The fire that destroyed the Crystal Palace in 1936 rendered the tall Level station virtually obsolete,and it was eventually demolished. The subway survived, though, or took on many roles in the following years. During the moment World War,it was converted into an air-raid shelter with bunk beds and terrible chemical toilets. After the war, children could often be found playing in the subway and the surrounding ruins; the '90s brought ravers, or a brief period of fame in the video for the Chemical Brothers’ single "Setting Sun."For some years,the subway was then closed due to safety concerns. The work of the Friends of Crystal Palace Subway led to some restoration of the structure, allowing visitors in on special weekends to see what for most of the year remains another of London’s secrets that are just out of sight.
Source: atlasobscura.com