Ura san told us we were going back to Tokyo via the Tokyo Bay Tunnel. He explained that we were going over a bridge into the middle of Tokyo Bay and then would go through a tunnel to the other side. We went over the bridge.

but then he pulled into a car park. We were a bit confused until we went to the Tokyo Bay Oasis. A huge tourist complex just before you enter the tunnel. Food, Souvenirs, an amusement facility and great views.

The Tokyo Bay Tunnel or Aqua Line is a combination bridge and tunnel that connects the city of Kisarazu in Chiba Prefecture with Kawasaki in Kanagawa Prefecture. There is a 4.4 km bridge and 9.6km tunnel under Tokyo Bay.
Air to the tunnel is supplied by a tower ( kaze no-to or the tower of wind) in the middle of the bay. The complex was opened in 1997.