Arithmeum Bonn

If memories of math class give you nightmares, this museum may not be for you. If they don't, you may well find this expansive collection of mechanical calculating machines – from the abacus to early computers by Hollerith and Babbage – quite fascinating. The science aspect is complemented by changing art exhibits, usually with a geometric constructivist bent. Work your way down from the top floor of the large minimalist glass-and-steel cube.