Greenwich foot tunnel
The 502nd longest tunnel in the world
The Greenwich Foot Tunnel crosses beneath the River Thames in East London. The southern entrance is by the Cutty Sark in Greenwich (Royal Borough of Greenwich), with the northern entrance located at Island Gardens, a park at the southern tip of the Isle of Dogs (London Borough of Tower Hamlets). Approximately 4,000 people use the tunnel (open 24/7) each day. It opened in 1902.
Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).