We were offered a National Park pass about 20 years ago during a visit to Mammoth Caves with our two grandsons. The older grandson has special needs and a Park Ranger at the Visitor Center gave us one, no questions asked. We've used it extensively since then, our original National Parks Passport is completely filled with stamps. We also use the pass at Corps Of Engineers campsites during our annual 2-3 month wanderabouts, it gives us a 50% discount on camping fees.