The Thames Tunnel is a historic underwater tunnel that runs beneath the River Thames in London, England. It was constructed between 1825 and 1843 and was the first tunnel ever built under a navigable river. Designed by engineer Marc Isambard Brunel, the tunnel was initially intended for horse-drawn carriages and later adapted for pedestrian use. The tunnel stretches approximately 1,300 meters (4,300 feet) and connects the areas of Rotherhithe and Wapping. Today, it serves as part of the London Overground network, providing an important transportation link for commuters and visitors in the city.