Denmark Is Building the World's Longest Immersed Tunnel — Here's How

In May 2026, a concrete block longer than two football pitches and weighing 73,500 tonnes was lowered into the Baltic Sea. It is the first of 89 elements of the Fehmarnbelt Tunnel, the road and rail link between Denmark and Germany that is under construction right now. This film explains how an immersed tunnel works, why Denmark and Germany chose a tunnel over a bridge, what happens in the Rødbyhavn element factory, how elements are lowered onto a gravel bed with millimeter precision, how fire and ship hazards are handled, and why the original 2029 opening is no longer realistic. Status note: the tunnel is not finished. Femern A/S has not published a new opening date. The road is planned to open first and the railway later. Any year mentioned for the road opening in this film is a press estimate, not an official date. Chapters 0:00 The block that sank 1:43 The strait and the promise 3:47 Bridge or tunnel 5:27 How an immersed tunnel works 8:20 The element factory 12:17 Trench, foundation and new land 15:46 Immersion day 20:54 Why it is late 25:05 Law and politics 26:50 Fire, ships and pressure 29:54 Comparisons and money 32:30 Where it stands in October 2026 Sources Femern A/S fact sheet, August 2026: https://femern.com/media/03kk5d0x/260... Femern A/S news: https://femern.com/press/news/ Femern A/S, a safe link: https://femern.com/the-tunnel/a-safe-... Federal Administrative Court, judgment of 3 November 2020: https://www.bverwg.de/en/031120U9A12.... Sund & Bælt, safety in the tunnel: https://sundogbaelt.dk/en/road-and-ra... Images: diagrams are original illustrations; photographs are documentary stock images; any visualisations are labelled as such. Visuals are illustrations and explanatory diagrams created for this video, not original footage.