A scaled-down model of the solar system installed in granite monuments down the Ithaca Commons. Start at the sun (a large globe on State Street) and walk three-quarters of a mile out to the Sciencenter, where Pluto sits demoted but defiantly included. Each monument shows the planet at the correct relative size and distance.
It takes about twenty minutes to walk the whole route. Pick up a free Solar System Walk Passport at the Sciencenter or at any of the marker sponsors and get it stamped at each planet — the souvenir is more satisfying than it has any right to be.