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Yellowstone was the world's first National Park established in 1872, and is one of the largest parks inside the United States. The Grand Loop Road is over 150 miles long and goes by Lake Yellowstone, Yellowstone Falls, Old Faithful and Hayden Valley.
The Park is full of wild animals including grizzly bears, grey wolves, american bison, black bears, elk, pronghorn, moose, and so much more. It is very common to come upon a herd of bison right next to the road, but other animals such as grey wolves are a very rare sight to see. Grey wolves don't come near the road hardly at all, so consider yourself extremely lucky to view one of these creatures even from a half a mile away. In Lamar valley there are a couple spots where you can see the wolf dens from a very safe distance, so remember to bring a good pair of binoculars. Lamar Valley and Hayden Valley are the best places to view wildlife, but make sure to ALWAYS keep a safe distance away from any of the wildlife.
One of the most recognizable images of Yellowstone is Old Faithful. Old Faithful goes off about every 45 minutes and there is usually a very large crowd of people surrounding the geyser. Around the Old Faithful area there are plenty of other smaller geysers to view. Make sure to stay on the boardwalks, because the water coming out of these geysers is extremely hot and WILL burn you. In fact, Yellowstone is the world's largest super volcano, which is why there are so many geysers and hot springs throughout the park.
Yellowstone is a magnificent place, but always make sure you are respectful of the wildlife and natural beauty.