Artists Paint Pots, Yellowstone National Park.

Be sure to stop here before leaving the park, you won't be disappointed.This place has all of the four types of hydrothermal features. You can see small geysers, fumaroles (loud steam vents), mud pots, and boiling springs. The bubbling mud was fun to see (and hear).
The colors are truly splendid.  It is almost like a moonscape with beautiful colors. Nature surely is amazing.

Three miles south of Norris Geyser Basin, the equally large but generally less active Gibbon Geyser Basin contains several dispersed collections of thermal features of which the most popular is Artists Paint Pots, a group of over 50 springs, geysers, vents and especially mud pots.
These exhibit varying shades of blue, grey and brown, and have a range of different textures, with the behavior changing during the year depending on the amount of subterranean water.

The bubbling mud was almost mesmerizing, bubbling up and shooting globs of mud in the air.