Yellowstone has more thermal features -- geysers, mud pots, and steam vents -- than the rest of the world combined. When you're angling for a good shot of a colorful pool or a belching mud pot, obey the signs -- otherwise, you could find yourself, literally, on shaky ground.
- Old Faithful Geyser: While not quite as faithful as it used to be -- the intervals average 74 minutes but sometimes stretch as long as 120 minutes -- it's still the most predictable geyser on the planet, blasting water 130 feet into the air more than 20 times a day. How could you skip this one?
- West Thumb: This lakeside thermal area is a must-stop for its collection of gemlike hot pools and steaming vents, as well as Fishing Cone, where early visitors poached their catch -- until they realized the scalding water had natural traces of arsenic.
- The Riverside Geyser: This beauty sits on the bank of the Firehole River and sends 75-foot columns of water arching over the river.
