Norway's dramatic coastline is famously breathtaking, but driving along the E39 coastal highway requires endless ferry trips because the fjords are ridiculously deep and wide. The Sognefjord, for instance, is over 4,000 feet deep and nearly a mile wide, making traditional suspension bridges or seabed-resting tunnels practically impossible to build. Enter the Submerged Floating Tunnel, also known as an Archimedes bridge.
Instead of resting on the seafloor or hanging above the waves, this engineering marvel floats entirely underwater, suspended around 100 feet beneath the surface. The magic relies on basic physics: Archimedes' principle. The hollow concrete twin tubes displace enough water to create massive upward buoyancy.
To keep the tunnel from rocketing to the surface like a mega-sized pool noodle, engineers anchor it to the bedrock deep below with heavy tension cables, or attach it to floating surface pontoons. By keeping the structure submerged at a precise depth, it dodges harsh Arctic storms, crashing waves, and extreme weather, while staying deep enough to allow ship traffic to pass safely overhead and high enough to avoid abyssal ocean pressures. While no full-scale submerged floating tunnel has been completed yet, Norway's ambitious $47 billion infrastructure project could soon turn these buoyant underwater highways into reality, revolutionizing fjord transport forever.