Yellowstone, the first national park in the world, was established by the U.S. Congress in 1872 and has welcomed millions of visitors in the 139 years since. Last year, Yellowstone recorded its highest number of visitors ever, as some 3.6 million people passed through its gates. Its well-known geothermal features -- geysers, hot springs, and fumaroles -- owe their existence to the massive Yellowstone Caldera, a 45-mile-wide volcanic system beneath the park. Tourists are also drawn to Yellowstone's hundreds of species of wildlife, massive waterfalls, and incredible vistas. Collected below are a few recent views of Yellowstone National Park. A bull elk with velvet still on its antlers grazes near Madison. A bison rubs scratches itself against a fire hydrant to help remove molting fur, outside the Mammoth Hot Springs Hotel in Yellowstone National Park, on May 15, 2011. The Grand Prismatic Spring, the largest in the United States and third largest in the world, in Yellowstone National Park.