London/New York transatlantic tunnel.

Inside the incredible £15.6 trillion Transatlantic Tunnel that would connect England with America in 54 minutes, the idea of a tunnel linking England with America has been kicking around for over a century, with the infrastructure project set to cost an eye-watering £15.6 trillion.

https://metro.co.uk/2024/12/10/a-15-000-000-000-000-tunnel-might-soon-link-new-york-london-22158872/amp/