Seikan Tunnel

The Seikan Tunnel is like a really long, secret tunnel that goes under the ocean! It's in Japan and it's really special because it connects two big islands, called Honshu and Hokkaido. It's SO long that if a train started in Honshu and went all the way through the tunnel to Hokkaido, it would take about an hour!

The tunnel is special because it was built under the ocean, which is really, really deep and full of water. And the water can be very dangerous for things that are made out of metal, like trains. So the builders had to be really careful to make sure that the tunnel was strong and safe, even while it was under the ocean!

To make it, the builders used a special drill that dug down into the sea floor so they could make a "pit" for the tunnel to go in. Then, they put these big metal panels (called "segments") together to make a big tube. Finally, they put the tube into the "pit" and sealed it up really tight, so no water could get in.

Once the tunnel was all done, they added train tracks and some trains to go through it! Now, people can take the train from Honshu to Hokkaido, and they don't even have to go around the ocean anymore!