Islington Tunnel
London Borough of Islington, United Kingdom · built 1818
The Islington Tunnel takes the Regent's Canal 960 yards (878 m) under Islington, as the longest such tunnel in London. The way for short boats and barges only opened in 1818; the pavements above are waymarked so the otherwise discontinued towpaths are connected. The canal's Eyre's and Maida Hill Tunnels, to the west, are much shorter.
Canal data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).