Yellowstone is based on a combination of three elements. First, are the ten thousand active geothermal features, geysers, hot springs, fumaroles, and mud pots, which are found over one third of the park, in a area that was several thousand years ago part of the of a huge volcano. The majority of these areas are located close to the main roads so are easy to visit though there are plenty lesser known regions in the backcountry. One half of all such features on Earth are found within the park, are nearly 50% of all geysers Yellowstone National Park has around 450 of these, out of a worldwide total of 970. Secondly, the park has beautiful mountain scenery, with high peaks, forceful rivers flowing through steep sided ravines and over frequent waterfalls and cascades, the 130 square mile Yellowstone Lake plus many smaller lakes, and the Grand Canyon of the Yellowstone River. This is the largest canyon in the park, 20 miles long and up to 1,000 feet deep.
The third component is the wildlife. Yellowstone National Park is the last place in the USA where bison still roam in their natural state, and has the greatest concentration of grizzly bears south of Canada. The park has several hundred wolves. There are many more black bears, together with elk, moose, deer, bighorn sheep, and numerous smaller species.
Park roads are generally good, though despite its large size, Yellowstone can become crowded, especially at popular places like Upper Geyser Basin