Zothecula writes: Though the idea of sleeping inside a concrete tube probably doesn't sound that appealing, architect firm T3arc have found a way to make sleeping inside a pipe not only comfortable but also a holiday experience. Mexico's Tubohotel, which opened in 2010, is a unique and affordable holiday destination created from recycled concrete tubes. Located approximately 45 minutes south of Mexico City in the village of Tepoztlan, Morelos, the rooms of the hotel are stacked in a pyramid shape, reflecting the Aztec pyramid of El Tepozteco that overlooks the town.
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"