The Thames Tunnel was the first tunnel known to have been constructed successfully underneath a navigable river. It was built between 1825 and 1843 using Marc Isambard Brunel’s and Thomas Cochrane’s newly invented tunnelling shield, by Brunel and his son Isambard Kingdom Brunel. The full story can be seen at https://en.wikipedia.org/wiki/Thames_Tunnel
The tunnel is now used by London Overground trains – see https://www.geograph.org.uk/photo/6487327
The story of the Thames Tunnel is told at the Brunel Museum – see https://www.thebrunelmuseum.com/ This garden is on top of the capped south shaft to the tunnel.