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This Foucault Pendulum is at the University of Heidelberg in Germany.

A Foucault Pendulum (pronounce foo-koe) is a fascinating physics device which demonstrates the the rotation of the earth on its axis. They are mesmerizing displays. I still vividly remember the one I observed in 1970 at California Academy of Sciences.

Typically, at the outer arc of the swings, the pendulum ball knocks over a small peg. Over a period of time (depending on the latitude of the installation) the pendulum will knock down all pegs - demonstrating the full circle of earth rotation.

Wiki article describing Foucault Pendula.

Simthsonian article for those who don't trust Wikipedia.