Float On

This "floating tunnel," from 1971, was meant as a new kind of "ship-to-shore roadway or an emergency bridge."

[Image: Floating tunnel, via Modern Mechanix].

I think, though, that it'd be more interesting as a walkway between Glen and Roonah Quay, or from Nyord to Stege Bugt.
Or build six dozen of these off the southern tip of Manhattan, connect them all up somehow, and open a nightclub. It glows at night on the horizon, full of dancing silhouettes, and distant music can be very faintly heard over the waters. Kids see it and think they're dreaming. Friendly whales nudge it with their heads as they swim back out to sea.
You then franchise the club to London, Berlin, and Rome, where it floats down the Thames, Spree, and Tiber rivers, respectively.
The Guggenheim soon opens a new overseas branch of their museum inside a custom-made tunnel; it is dedicated to performance art and anchored in the middle of Lake Victoria.
Inspired, three restless Goethe scholars from Columbia University purchase one off eBay and turn it into a mobile writing lab, which they take with them on a leisurely summer tour of the Rhine. They grow beards, sleep inside the tunnel, and write books about European natural history; six months later, they appear on Oprah.
I'm in the audience that day, and I stand up and ask: "Did you get that idea from reading BLDGBLOG?"

(Via Modern Mechanix).