London Mithraeum

The lowdown

London Mithraeum, the Temple of Mithras, is free to visit with a timed ticket booked online. When builders dug the foundations of a new office in 1954 they uncovered this Roman temple to a secretive cult god worshipped by soldiers and merchants in the third century, and Bloomberg rebuilt the whole thing on its original site, seven metres below the modern street.

Down in the cool dark you stand among the reconstructed temple walls while a clever light and haze show conjures the lost ritual back to life, complete with the murmur of voices. It is part archaeology, part theatre, and genuinely atmospheric.

Upstairs a wall displays hundreds of Roman objects pulled from the Walbrook mud, including the famous writing tablets that carry the oldest known handwriting from Britain. For a free hour in the City it is hard to beat, just remember to book ahead.