Located principally in northwestern Wyoming and extending into southern Montana and eastern Idaho, the Yellowstone National Park contains the greatest concentration of geothermal features in the world, which include the famous Old Faithful Geyser. Established by the US Congress on the 1st day of March 1872, it is the oldest, one of the largest and probably the best known national park in the country, offering spectacular hiking trails, wonderful scenic beauty, geysers shooting water 100 feet into the air, colourful hot springs, mud pots and breathtaking waterfalls. Although generally considered to be the first national park in the world, it is also argued by many that Yellowstone was predated by the creation of Bogd Mountain National Park in Mongolia, which in all possibly may date from as early as 1778.

It is estimated that the human history of the park began around 11,000 years ago when Native Americans began to hunt and fish in the region. However, American trapper and explorer John Colter is the first person, who after leaving the Lewis and Clark Expedition in 1806, ventured into the Yellowstone region during the winter of 1807–1808 and observed at least one geothermal area in the northeast section of the park. However, his description of a place of fire and brimstone was mostly dismissed as delirium, although the supposedly mystical place was nicknamed Colter’s Hell.

Over the next two decades, reports of other trappers like Jim Bridger, Joseph Meeks and Osborne Russell, about observing boiling springs, spouting water, a lake and a mountain of glass and yellow rock, were also largely ignored.

Nevertheless, the first published account of the region appeared in a Philadelphia newspaper in 1827, containing a letter by Daniel Potts to his brother, vividly describing Yellowstone Lake and the West Thumb Geyser Basin. Finally, in 1836, Warren Angus Ferris, a trained surveyor, visited Yellowstone and was the first to use the name geyser for the hydrothermal features in the region and prepared a map of the Yellowstone area. Despite an official government party led by Capt. William F Raynolds failed to reach Yellowstone in 1860, the well-planned Washburn-Langford-Doane and Hayden expeditions of 1870 and 1871, successfully undertook extensive   surveys of the region.

The team spent about a month in the region, exploring and collecting specimens and naming sites of interest. It was Hayden, who realized that Yellowstone is a treasure trove, commercially viable for recreation and strongly advocated for the creation of a national park at Yellowstone.

Covering an area of 3,472 square miles (8,992 sq km), Yellowstone National Park forms a squarish rectangle with an irregular eastern side, spanning 54 miles (87 km) from east to west and 63 miles (101 km) from north to south. Situated in a region that has been volcanically and seismically active for tens of millions of years, the park comprises lakes, canyons, rivers, mountain ranges, more than half of the world's geysers and hydrothermal features, fuelled by the continued volcanism. The Caldera, considered a dormant volcano, had erupted with tremendous force several times within the last two million years. It is maintained that about 2.1 million years ago, a subsurface magma dome that had been building up in the Yellowstone area, blew up in one of the most cataclysmic volcanic eruptions of the world, when some 600 cubic miles (2,500 cubic km) of rock and ash were ejected. Lava flows and rocks from those volcanic eruptions cover most of the land area of Yellowstone.

The Yellowstone Lake, covering a surface area of 132 square miles (342 sq km), is the largest body of water in the park, lying at an elevation of 7,730 feet (2,356 m), one of the largest high-elevation lakes in North America, centred over the Yellowstone Caldera, the largest supervolcano on the continent. Shoshone Lake, the next largest lake, lies in the caldera southwest of Yellowstone Lake. The Yellowstone River, the most extensive drainage system of the park, enters at the southeast corner, flows mostly northward through the Yellowstone Lake and exits near the northwest corner of the park.

The Yellowstone Falls, located in the north-central part of the park, descend in two majestic cascades, namely the Upper Falls, with a drop of 114 feet (35 m) and the Lower Falls, with a drop of 308 feet (94 m). The falls constituted the western end of the spectacular Grand Canyon of the Yellowstone, where a 19 miles (30 km) long gorge is created by the steady incision of the river, which is  800 to 1,200 feet (240 and 370 m) deep and up to 4,000 feet (1,200 m) wide. The walls of the canyon, stunningly coloured with various hues of red, pink, yellow, buff, lavender and white, create a surreal beauty, which is hard to believe.

However, the chief attractions of Yellowstone Park are its numerous hydrothermal features, consisting of colourful hot pools, mud cauldrons, fountain paint pots, hot springs and terraces, hot rivers and geysers. The park contains more than 300 geysers, more than half of the world’s total, many of which erupt to heights of 100 feet (30 m) or more. The greatest concentrations of the geysers are in the Upper, Midway and Lower Geyser basins, located in the western portion of the park. Located in the Upper Geyser Basin, the Old Faithful Geyser, perhaps the most famous geyser in the world, erupts pretty regularly, roughly every 90 minutes with a range of reasonably predictable variability. However, the Steamboat Geyser is the world’s highest-erupting geyser that can throw water to heights of 300 feet (90 m) and higher. Apart from that, the park includes the Giantess Geyser near Old Faithful, Excelsior Geyser in the Midway Geyser Basin, the deep-blue Morning Glory Pool just to the northwest in the Upper Geyser Basin and the Fountain Paint Pots in the Lower Geyser Basin, along with the pink, plopping mud geysers, the Grand Prismatic Spring, Fumaroles or steam vents, the gurgling mud pots and a blue hot-spring pool.

Apart from the geothermal features, about four-fifths of the park’s area is forested, hosting the greatest assemblage of mammals, which include bison, wapiti, brown bears, black bears, foxes, mule deer, bighorn sheep, pronghorns, mountain goats and many more. However, adorned with numerous geysers, colourful hot springs, mud pots and breathtaking waterfalls, along with the multicoloured Minerva Terrace and Angel Terrace, consisting of dazzling white rock that in many areas is tinted by microorganisms, creating a surreal beauty, Yellowstone National Park was named a UNESCO World Heritage Site in 1978.