19 incredible photos that show why you should visit a national park this week
April 16th to 24th is National Park Week, meaning that admission to all national parks is free. This year also marks the National Park Service's centennial, as it was created on August 25th, 1916.
From the well-known geysers of Yellowstone to the labyrinthine tunnels of Mammoth Caves, we've rounded up some of the most awe-inspiring and unique features of national parks across the country. Now's as good a time as ever to check one out.