Fehmarnbelt Tunnel between Germany and Denmark, World's Longest Immersed

RailFreight
The 18km tunnel will remove 2 hours from the current 4.5 hour trip between Hamburg to Copenhagen. Consequently, it also removes 2 hours from trips between Hamburg and the Scandinavian countries. Construction should finish by 2029. The 7.1 billion euros project has a repayment period of 36 years.

RailFreight
The tunnel will be built using cut&cover with 89 "elements." It will have four lanes and two tracks.

Screenshot @ 0:46, cropped

https://youtu.be/VnISluP-ZO8?t=254 4:14

If you want to skip the rather obvious economic arguments for the tunnel in this 14:33 video, then start here. From 7:16, I skipped to 8:10 about construction options.

8:41 video

This 3:32 video about the sealant contains some construction scenes.

A 3:18 video of an animation of the construction process.

 This 4:02 animation video includes a narration and is easier to understand.

Aaron Witt's videos: 17:02, 21:52

safe_image for The new $7.4 billion underwater tunnel connecting 2 major countries will halve rail time

I think many of the scenes in this video are from this tunnel.

Amazement Show posted
How is an underwater tunnel built?

Oct 2026: The two gantry cranes were two years late. As of late Sep 2026, four of the segments have been placed.

15:12 video @ 7:57
The Fatal Flaw Threatening Europe’s €10B Megaproject
I think the flaw is that the railroad in Germany that is supposed to connect to the tunnel will cost more than the tunnel itself and it will take years to build.