George Hart writes:
Michigan artist David Barr designed his "Four Corners Project" in 1976. It is an Earth-sized regular tetrahedron that spans the planet, with just the tips of its four corners protruding. These visible portions are four-inch tetrahedra, which protrude from the globe at Easter Island, Greenland, New Guinea, and the Kalahari Desert. Barr traveled to these locations and was able to permanently install the four aligned marble tetrahedra between 1981 and 1985.
Glad to see someone's already done it! Though I should say I liked Dan Asimov's idea of using cylindrical tubes, which wasn't part of Barr's conception (and probably couldn't have been, given mid-70s technology). Michael Kleber writes:
I think the four "tetrahedron vertex" sculptures sounds like an outstanding art project. If none of Jim's suggestions work, surely there's someone who made far too much money in the dot-com boom, who's just sitting around waiting to fund something like this!
If there's some mathematically inclined dot-com zillionaire out there (a Google googolionaire, perhaps?) who's looking for something else fun to build, might I suggest a scaled-up, climbable version of the Boy's Surface sculpture at Oberwolfach? Jim