Osmium is both the densest and the rarest element that you can dig out of the Earth. It's so hard that it's used (as an alloy) in places with constant pressure and wear, like the tips of fountain pens. One single cubic inch of this stuff weighs nearly a pound, and were you to somehow get a cubic foot of it, it would weigh over 1,400 pounds. Good luck with that, though: last year, the entire U.S. osmium production was only 165 pounds.
This 208 sq.ft. tiny house on wheels includes a split level loft, balcony, and -- not something we can say often in a tiny house description -- a walk-in closet! The kitchen has a 9.2 cubic foot refrigerator and 4 burner range with oven.