[gunzel412]

Let me introduce you to the Seikan Tunnel [1] between the islands of Honshu and Hokkaido in Japan, 53.85km with 23.3km of that under the sea.

[1] https://en.wikipedia.org/wiki/Seikan_Tunnel

[ChrisMarshallNY]

Now, that’s scary. I do know that the Japanese have the world’s best anti-earthquake architecture (because they need it), but it’s still scary.