SCUBA diving fascinates me. Considering that 3/4ths of our planet is covered by water, land-locked critters only see a fourth of it all our lives, even if we travel to rainforests, mountain peaks, deserts, plains, and swamps.
When on land I like history, so I haunt museums, old cemeteries, battlefields, and other historic places. Recently I went to a reenactment where they had a battle, authentic military camps (Yankees and Rebels), and even a Victorian Ball where we did dances of the period.
Did you know that a drummer boy (and a bugler) didn't just play to boost morale or set the pace for marching, but actually conveyed information and orders to troops during battle? Like being in the Signal Corps, only on the battlefield getting shot at and everything!