Thames Tunnel (1825)

The entrance you see here leads to the Thames Tunnel, the first tunnel ever built under a navigable river. When engineers Marc and Isambard Kingdom Brunel started digging in 1825, most experts said it was impossible. They were almost right.

The tunnel flooded on 18 May 1827 after workers accidentally broke through into the riverbed. Isambard Brunel dove down in a diving bell and plugged the hole with bags of clay. Then he threw a banquet inside the drained tunnel to prove it was safe.

It flooded again on 12 January 1828. This time, six men died. Isambard himself barely escaped, pulled unconscious from a locked emergency exit. The project stopped for seven years. No money, no investors, nobody believed anymore.

They finally finished in 1843 after 18 years of work. It cost £634,000, triple the original estimate. The tunnel was designed for horse carriages but they never came. Instead, it became a tourist attraction. Two million people per year paid a penny to walk through. Shops and fortune tellers set up inside. Americans called it the eighth wonder of the world.

In 1869, they converted it into a railway tunnel. Trains still run through it daily as part of the London Overground.