Chislehurst Caves

Twenty-two miles of hand-dug chalk tunnels lie beneath Chislehurst, and families explore them by oil-lamp on a guided tour. Guides weave together centuries of history — chalk and flint mining, a First World War ammunition store and, most memorably, the vast air-raid shelter where thousands of Londoners sheltered during the Blitz, complete with its own chapel and hospital.

Expect ghost stories, echo tricks and plenty of “turn your lamp off” moments that kids talk about for weeks. It is cool underground all year, so it works as well on a scorching day as a rainy one.