Originally completed in 1664, the 10-foot-diameter German contraption has a hollow interior, painted with constellations, that you can enter. The design inspired the modern planetarium. It’s now on display at the Kunstkamera museum, in St. Petersburg, Russia.
The world is flat: Viewed from a certain angle, “land artist” François Abélanet’s ingenious trompe-l’oeil installation (recently in Paris) seems to take the shape of a sphere. His works, always temporary, are meant to play with the environment without disrupting it.