Londinium was founded in 43 CE and the city has never stopped building on top of itself. This route goes down to the Mithras temple under Bloomberg, into the Templars' round church, and beneath Whitehall to the room where 1940 was fought.
William the Conqueror raised the White Tower in 1078 to cow the Saxon city; the fortress later held the Crown Jewels, Anne Boleyn and the Kray twins. Opens 09:00 Tue–Sat, 10:00 Sun–Mon, from £35 online.
The temple of Mithras was uncovered in a 1954 bombsite and now sits seven metres down at its original Walbrook level, under Bloomberg's HQ. The reconstruction runs 20 minutes with mist, torchlight and Latin chant.
Builders digging in 1988 struck the arena where Londinium watched gladiators from about 70 CE. The black stone entrance walls survive in the gallery basement, ringed by a fibre-optic outline marking the vanished seating.
Consecrated in 1185 by the Knights Templar, the round nave copies the Holy Sepulchre in Jerusalem. Nine armoured effigies lie on the floor, among them William Marshal, regent of England and guarantor of Magna Carta.
The Cabinet met 115 times in this basement below Whitehall. The complex was locked in August 1945 and opened largely untouched in 1984; pins in the Map Room still track Atlantic convoy routes as they stood on the last day.
Wren and Hooke's 62-metre Doric column stands exactly 202 feet from the Pudding Lane bakery where the 1666 fire started — the height matches the distance. It is 311 steps to the caged viewing platform.
Built in 1815 as Bethlem hospital — the original 'Bedlam' — and converted to the IWM in 1936. Two 15-inch guns from HMS Ramillies guard the door; the Holocaust Galleries and the Second World War floor anchor the collection.
Wren's 1697 steeple rode out the Blitz; the nave did not. The City planted the roofless shell as a public garden in 1971, and fig trees and Virginia creeper now climb through the empty Gothic window tracery.
A Spitalfields terrace staged as if a family of Huguenot silk weavers stepped out mid-meal in 1724 — half-eaten bread, unmade beds, chamber pots, guttering candles. Ten rooms, no labels, no electric light.
The oldest surviving grand music hall in the world, built in 1859 behind an 1820s sailors' alehouse in Wapping. A 1964 campaign led by John Betjeman stopped the bulldozers; the peeling walls were conserved, never restored.
The architect of the Bank of England left his Lincoln's Inn Fields house to the nation in 1837 on condition that nothing ever be moved. Hogarth's Rake's Progress hangs on folding walls; Seti I's alabaster sarcophagus sits in the crypt.
The 1504 gatehouse is the last stone of the Knights Hospitaller priory that once covered ten acres here. Around the corner on the Green, the Marx Memorial Library holds the office where Lenin edited Iskra in 1902–03.