When Sweden and Denmark built a connection between their countries, Sweden preferred a bridge, and Denmark preferred a tunnel, they each built their half and connected them in the middle with an artificial island. The Øresund Bridge is unique in the world.
There’s one in Virginia, the Chesapeake Bay Bridge Tunnel. There are two tunnels segments to go under major shipping channels. There are major naval bases upstream, and it was considered a national security risk to have a fleet potential trapped behind a downed bridge.
along with the Hampton Roads Bridge-Tunnel right next door
The Hong Kong-Zhuhai-Macau Bridge is another one. It’s a bridge most of the way but there’s one section that’s a tunnel.
I drove the Chesapeake Bay Bridge tunnel back in the 70’s with my mom on one of our trips.