In the nineteenth century the rivers on which Sheffield is built were polluted, insanitary and smelly.
The River Porter runs south-east to join the River Sheaf at the site of the city’s railway station, and the Sheaf then runs north-east for about a quarter of a mile to join the River Don at the site of the medieval castle.
Both rivers were progressively culverted, tidied away and largely forgotten about.
The original Midland Railway station, platforms 5-8 of the modern station, opened in 1870, and was more or less doubled in size in 1905 when the present concourse and platforms 1-4 were added.
It’s difficult to imagine, while waiting for a train, that beneath the tracks is a spectacular complex of vaults and arches carrying the water from the two rivers northwards under Sheaf Street, where there is a brief open stretch before the watercourse disappears under the Ponds Forge International Sports Centre, next emerging at the confluence of the Sheaf and Don at the end of the oddly-named Blonk Street (named after a scissor-smith, Benjamin Blonk).
This last section was only completed in 1916, after the demolition of the Alexandra Theatre a couple of years earlier. Part of the theatre building stood on iron columns over the river bed: http://www.arthurlloyd.co.uk/SheffieldTheatres.htm#alex. The now-defunct and possibly haunted Alexandra Hotel stands on an adjacent site: https://sheffield.camra.org.uk/2013/11/alexandra-hotel.
There are plans to remove the 1916 culvert as part of the forthcoming development of the former Castle Market site, and there are informal campaigns urging the opening of other stretches of Sheffield’s buried rivers.
An artful slide-show that suggests the cavernous extent of the area beneath the station (named for reasons which escape me the Megatron) is at https://www.youtube.com/watch?v=7fmsG6svhYo, and there is a coherent description with good photographs at substormflow – Megatron .
There is a spectacular video of waterborne gymnastics at the same location: https://www.youtube.com/watch?v=XlTcPuSvXQc.
And three more pedestrian urban-explorer reports are at https://www.28dayslater.co.uk/threads/river-porter-culverts-sheffield-railway-station-april-2017.108056, https://www.youtube.com/watch?v=T13hCT2XBn4 and https://www.28dayslater.co.uk/threads/megatron-sheffield-june-and-july-2015.97955.
Brighton opened its sewers to public tours half a century ago: https://www.southernwater.co.uk/brighton-sewer-tours. Perhaps Sheffield should open its subterranean rivers.