Mail Rail 
Description
The Mail Rail was a small narrow gauge automatic railway designed for quickly sending post across the capital deep beneath the streets, avoiding the congestion above. Mail Rail itself closed in the early 2000s and there were several ideas of what to do with the abandoned tunnels that stretch for around 7 miles under the centre of London. Today the network is maintained in a moth-balled state, in case a use can be found for it, but a small section around the Mount Pleasant sorting office is now open to the public to explore on a 15 minute ride in specially adapted mail carts (the railway was never built with the intention of humans riding on it - so the carriages are small and very cramped)
Charge
Charge, Includes Postal Museum
Getting There
Latitude: 51.524547; Longitude: -0.113367
What3Words: potato.backup.jolly
