Our state parks may not boast volcanoes and rainforests, but the 110-year-old system holds just about everything else under our intermittently visible sun: caves and campsites, fossils and forts, dive sites and, well, death tolls. We have rental teepees and historic Native American art, adventure sports and museums. Even better? Almost all of it is free after a $30 Discover Pass. From our half-acre pocket parks to cross-state trails, the state park system is a whole different kind of wild.