(CNN)There are 2,000 years of history woven deep into the fabric of London.
From the tip of the Shard -- the city's tallest building, which opened in 2013 -- to the ancient "lost" River Fleet that still flows through the British capital's underground sewer network.
Subterranean London is a world of mausoleums, secret bunkers, lost rivers, abandoned train stations and twisting tunnels.
Here are four of the coolest underground spaces just below the city's surface:
Roman Amphitheater, Guildhall Art Gallery
The ruins of a Roman amphitheater, from AD 70, were discovered under Guildhall Art Gallery in 1988.
The amphitheater hosted wild fights and executions and could hold more than 7,000 spectators.
Gordon's Wine Bar
Gordon's is the city's oldest wine bar, in the atmospheric setting of a vaulted cellar. It still has its original decor from 1890.
Churchill War Rooms
Under the streets of Whitehall, Prime Minister Winston Churchill and his cabinet gathered in this secret bunker to orchestrate World War II.
Many of the rooms have been left exactly as they were in August 1945, the day Japan surrendered and the war was declared over.
A former morgue in the tunnels under Waterloo Station, this 17,000-square-foot space is now a multi-purpose arts venue, with a gallery, theater and restaurant.