TOP 3 TOURS UNDER THE CAPITAL

1The Mail Rail once ferried 4 million letters a day below London. But after 75 years it closed, only to be resurrected as a ride in 2017. Whizz its tunnels in a tiny train ( top) as its history is told on film across the walls (postalmuseum.org; £17).

2 Hidden London tours have led visitors around abandoned tube stops, through lost tunnels and even into Churchill’s bombproof secret station. The settings change with each new batch of visits released – watch out for the latest in January (ltmuseum.co.uk).

3The hand-dug tunnels of Chislehurst Caves (chislehurst-caves.co.uk; £6) stretch 35km. Tours explore a fraction of that, but let you explore its past as a medieval chalk mine, a shelter for 15,000 during the Blitz, and a cult music venue (Bowie

and Hendrix played here).