Short answers, pulled from the story.
The Thames Tunnel was built by Marc Brunel and his son Isambard Kingdom Brunel, using a tunnelling shield patented by the elder Brunel in January 1818. Construction ran from February 1825 to November 1841, and the tunnel opened to the public on the 25th of March 1843.
The Thames Tunnel is a tunnel beneath the River Thames in London, connecting Rotherhithe on the south bank to Wapping on the north. It measures 35 feet wide by 20 feet high and runs 1,300 feet long at a depth of 75 feet below the river surface at high tide.
Digging the Thames Tunnel cost £454,000, and fitting it out cost an additional £180,000, both figures far exceeding the original estimates. The Treasury provided a loan of £247,000 in December 1834 to allow construction to resume after years of stoppage.
The Thames Tunnel was the first tunnel successfully built beneath a navigable river. It demonstrated that underwater tunnelling was possible despite widespread professional scepticism, and it directly inspired the construction of subsequent tunnels including the Tower Subway, the Severn Tunnel, and the Mersey Railway Tunnel. In 1991 it was designated an International Historic Civil Engineering Landmark.
The East London Railway Company purchased the tunnel in September 1865 for £800,000. The first train ran through on the 7th of December 1869. The tunnel is now part of the London Overground network and reopened in that capacity on the 27th of April 2010.
The Thames Tunnel is in active use by London Overground trains and is not routinely open to the public. London Transport Museum occasionally organises walking tours when engineering works provide sufficient access; the tunnel has held tours three times in the last twenty years as of 2025. The nearby Brunel Museum in Rotherhithe is open to visitors and includes the original engine house.