There's more about the City + South London tunnels, but the best I can find at the moment is this: > The original running tunnels north of Borough station rema

There's more about the City + South London tunnels, but the best I can find at the moment is this: > The original running tunnels north of Borough station remain, although when the Jubilee line extension was built in the late 1990s, the old southbound tunnel was cut through as part of the construction works at London Bridge station in order to provide the lift shaft situated at the south end of the Northern line platforms. These running tunnels are now used as a ventilation shaft for the station and the openings for several adits to the old running tunnels can be seen in the roofs of the Northern line platform tunnels and in the central concourse between them. A construction shaft between London Bridge and King William Street, beneath Old Swan Wharf, now functions as a pump shaft for the disused sections of the running tunnels. It is no longer possible to walk through between the two stations as the old C&SLR running tunnels have been blocked off with concrete bulkheads on both sides of the Thames. The tunnels were further severed by upgrades to Bank station, as the construction shaft for the new Northern line tunnel, located in Arthur Street, cuts straight through the approach tunnel to King William Street station, with the station site itself linked to the new tunnel via a ventilation adit.[4] https://en.wikipedia.org/wiki/King_William_Street_tube_station https://en.wikipedia.org/wiki/King_William_Street_tube_stati... IIRC there's also some other "tunnels" under the Thames around the London Bridge area that are old Victorian pneumatic pipes to deliver mail+parcels.