I have organized these slideshows from north to south.
YELLOWSTONE NATIONAL PARK
The Mammoth Hot Springs travertine terraces are a surface expression of the deep magmatic forces at work in Yellowstone. Although these springs lie outside the Yellowstone Caldera boundary, scientists surmise that the heat from the hot springs comes from the same magmatic system that fuels other Yellowstone hydrothermal areas.
You can find more information about this area of the park at the Mammoth Hot Springs NPS Page.
The Grand Canyon of the Yellowstone River expresses the park's complex geologic history in dramatic colors and shapes. Puffs of steam mark hydrothermal features in the canyon's walls. The Upper and Lower Falls of the Yellowstone River add to the grandeur of the unique natural treasure.
You can find more information about this area of the park at the Grand Canyon of the Yellowstone NPS Page.
Grand Prismatic Spring, located in Midway Geyser Basin, has the distinction of being the park’s largest hot spring. It measures approximately 370 feet in diameter and is over 121 feet deep. A description of this spring by fur trapper Osborne Russell in 1839 also makes it the earliest described thermal feature in Yellowstone that is definitely identifiable.
It is, for me, the most dramatically beautiful natural formation I have ever had the privilege to see and experience.
You can walk around the pool, or get a view from above via the Overlook Trail, just a few hundred feet south.
The Upper Basin, with Old Faithful, is the most visited area of the park. It features multiple active geysers, pools and other features.
There are many sites for geyser prediction. This one, at geysertimes.org is one of my favorites. You can also use the NPS Yellowstone Geysers app, or visit Yellowstone's geyser prediction Twitter feed.
You can learn more about the upper basin at the Upper Basin Yellowstone.net page.
Old Faithful is the most visited geyser in the world. It was named in 1870 by the Washburn expedition and it currently erupts every 92 +/- 10 minutes.
You can learn more about Old Faithful a the Yellowstone.net Old Faithful page.