Peak Season: Summer
Best time to visit: Summer - Winter
There are a dozen campgrounds located fairly evenly across this massive park
There's no question that Yellowstone would have been a five pinky up attraction had it not been for the abundance of tourists in this area. Now, Teddy Roosevelt said that these Parks are for the enjoyment of the people, it's just that we need all the people to not come at the same time. Plus, it's also a great example of American's love for their cars. Everyone drives up to everything, parks on the road to look at wildlife, and is typically in the way or at the very least not aware of the people around them.
So, Yellowstone is Old geezers and geysers galore. There are so many hydrothermal features in this park that it would take months to visit them all. There are several geyser basins (upper, lower, midway, norris, west thumb) all over the park. Many of the rivers flowing through the park are naturally warm or even hot thanks to the geothermal activity. Much of the park is speckled with steam spouts from the various geysers, hot springs, and steam vents. Finally, there's Old Faithful. It's kind of funny that there are bleachers set up and a schedule of eruptions for Old Faithful. Although, it's not particularly spectacular it's still a must see just because it is an icon of the park.
To me the greatness of Yellowstone is in its diversty. There are valleys where you can watch Bison graze. The Grand Canyon of the Yellowstone careens through the center of the park. Upper and Lower Falls serve as bookends to Canyon Village. There's also Yellowstone Lake. Dozens, if not hundreds of fly fisherman waded in the waters of the yellowstone hoping to catch a few trout.
There is an awful lot to do in Yellowstone and an awful lot of people trying to do the same things. It's one of the most unique locations I've seen in the US and a destination not to be missed.