Once you get into the geyser basin part of Yellowstone park you are able to walk out on elevated boardwalks over the many different hot springs, geysers, mud pots, etc.
I always find myself drawn to the trees that have been burnt by the geothermal events. The transitions from an almost bone type color to deep brown blacks. Very intriguing.
This photo is of a tree stumps that have been mostly bleached out.