[saalweachter]

I've wondered if you could build a stone pyramid -- using modern machinery -- financed as a time capsule.

For $X dollars, you can pay to have a cubic foot of stuff interred in the pyramid, for future historians to find. If a pyramid-sized pyramid can hold Y such lots, can you sell enough to pay for the construction?

It doesn't have to be anywhere specific, just pick a spot that's relatively dry and has appropriate stone nearby. Run it as a tourist trap afterwards to pay for whatever ongoing costs are needed to keep people from disassembling it for raw materials.