Panthéon

This guide to the Pantheon in Paris opens in 1851, when physicist Leon Foucault suspended a 28-kilogram brass pendulum from the dome and invited skeptical Parisians to come watch the Earth turn. It also traces the building's own reversals, from a church commissioned by Louis the Fifteenth in 1744, through the Revolution that turned it into a monument to Voltaire and Rousseau, and back again more than once. Listen with your eyes on the wire overhead, where a replica of that original pendulum still hangs.