The bridge on the red Kawasaki postmark is the Tokyo Bay Aqua-Line. It's a 4.4 km bridge and 9.5 km tunnel running across Tokyo bay, connecting Kawasaki to Kisarazu. In the background is Mount Fuji. And I believe what appears to be a sailboat on the left side of the postmark is actually the Tower of Wind. This structure supplies fresh air to the tunnel on the floor of the bay.