Imperial Geyser, Yellowstone National Park, Wyoming, United States

The most famous geyser in Yellowstone (and the world) is undoubtedly Old Faithful, but the battle with the crowds and the surrounding buildings give it a circus-like feel. This geyser is about 6 miles into the backcountry and goes off continuously, making for a flashy show; one that we didn't have to share with anyone!

Many of the bright colors found in Yellowstone's hydrothermal basins come from "thermophiles" —microorganisms that thrive in hot temperatures. So many individual microorganisms are grouped together—trillions!—that they appear as masses of color.

Different types of thermophiles live at different temperatures within a hot spring and cannot tolerate much cooler or warmer conditions. Yellowstone's hot water systems often show distinct gradations of living, vibrant colors where the temperature limit of one group of microbes is reached, only to be replaced by a different set of thermophiles.