Morning Glory Pool
If you were thinking that the neon green, yellow, and orange rings of color are quite unnatural for a Yellowstone Park site, you would be correct. In the 1940s, the Morning Glory Pool was an arresting shade of aquamarine. Unfortunately, those creatures called humans threw trash into this tiny pool, clogging vents that heated it - making it a simply a stagnant, brightly colored puddle. Throwing in a penny for good luck is ill advised, and will most assuredly get you at best a harsh reprimand from a park ranger.