Catherine Parker More than its star attraction (Old Faithful), the Upper Geyser Basin boasts not only the largest concentration of geysers in the park, but also in the entire world (Yellowstone is ...

U.S. News Insider Tip: Escape the crowds directly in front of Old Faithful and enjoy the geyser's eruption from the second-floor outdoor balcony of the Old Faithful Inn, another national treasure.

But along the Firehole River in the Upper Geyser Basin, snow melts faster ... The green is chlorophyll they use to absorb sunlight. Old Faithful throws a tower of steam into a moonlit sky.