Brunel's Thames Tunnel is an underground tunnel that runs beneath the River Thames in London. Designed by engineer Isambard Kingdom Brunel, construction began in 1825 and was completed in 1843. It was the first underwater tunnel in the world and was initially intended for horse-drawn carriages. The tunnel is approximately 1,300 meters long and connects the districts of Rotherhithe and Wapping. Although it faced numerous challenges, including flooding and financial difficulties, it eventually opened to the public and became a significant engineering achievement of its time. Today, it serves as a pedestrian walkway and is part of the London Overground network.