I've walked the Mackinac Bridge on Labor Day and it's really cool to stand on the grated section and see the water waaaaay down below you.

Unites Michigan's upper and lower peninsulas. The Mackinac Bridge is is the longest suspension bridge in the Western Hemisphere with 7,400 feet of roadway suspended in the air over the straits of Mackinac. Total length of the bridge, including its approaches, is approximately five miles.
The USA/Canada tunnel in Detroit dips under the river connecting Lake Erie and Lake St. Clair and only takes a couple minutes to traverse. Not that long at all.

I've always loved bridges and tunnels.