Mammoth Hot Springs is "one of the world's best protected examples of travertine-depositing hot springs ... Inactive terraces underlie most of this area, including under the Mammoth Hot Springs Hotel and the Albright Visitor Center." For great lighting, early mornings and later in the evening just prior to sunset are great times to visit and photograph the terraces and hot springs of this area.

"The Firehole River starts south of Old Faithful, runs through the Upper Geyser Basin northward to join the Gibbon River and form the Madison River. The Madison joins the Jefferson and the Gallatin rivers at Three Forks, Montana, to form the Missouri River." There's a bridge over the river, just prior to the turnoff to the Madison Information parking area, where you can watch the flow of the Madison River as it lazily makes it's way West. Look toward your right and you might even see a herd of buffalo grazing and lounging in the tall grass. 

According to the National Park Service, "Grand Prismatic Spring, located in Midway Geyser Basin, has the distinction of being the park’s largest hot spring. It measures approximately 370 feet (112.8 m) in diameter and is over 121 feet (37 m) 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."

You don't look a day over 100 (just kidding). "On March 1, 1872, Yellowstone became the first national park for all to enjoy the unique hydrothermal and geologic features. Within Yellowstone's 2.2 million acres, visitors have unparalleled opportunities to observe wildlife in an intact ecosystem, explore geothermal areas that contain about half the world’s active geysers, and view geologic wonders like the Grand Canyon of the Yellowstone River."