Happy 453rd birthday Galileo Galilei!
It may be slightly fanciful to believe that the man actually dropped a couple of different sized cannonballs from the leaning tower of Pisa but he certainly worked out that acceleration due to gravity does not depend on the mass of the object.
I remember visiting Pisa many years ago, before the tower was closed to visitors, and the weird feeling of climbing a spiral staircase that's tilted was an intriguing distraction from the oppressive Summer heat. The view from the top was wonderful and the thrill to think that the genius that was Galileo may have once stood at the exact same spot was well worth the sweat of the ascent. Much later Newton added some flesh to the bones of Galileo's ideas and then in more recent times Einstein polished them even further. In these days of the LHC we've been fortunate to witness even further refinements but lest we forget that the whole edifice of explanation rests on the shoulders of many giants, not least of whom was this persecuted (but brilliant) Pisan.