Yellowstone National Park

This massive log structure from 1904 is an attraction in its own right. Even if you don't spend a night at the Old Faithful Inn, walk through or take the free 45-minute guided tour to admire it. — Fodor's

Almost every visitor's itinerary includes the world's most famous geyser. — Fodor's

This stunning canyon is 23 miles long, but there is only one trail from rim to base. — Fodor's

The trail through Back Basin is a 1½-mile loop guiding you past Steamboat Geyser. When it erupts fully (most recently in 2014), it's the world's largest geyser, climbing 400 feet above the basin. — Fodor's

Artist Point is probably the most famous of the canyon’s viewpoints, offering a long overview of the Lower Falls and canyon. — Lonely Planet

The spring, in the Midway Geyser Basin, is deep blue in color, with yellow and orange rings formed by bacteria that give it the effect of a prism. Look down on it from the Fairy Falls Trail. — Fodor's

Biscuit Basin is named for biscuit-like deposits that surrounded stunning Sapphire Pool, but these were destroyed during violent eruptions that followed the 1959 Hebgen earthquake. — Lonely Planet

Built in 1931 as an information station for the first automobile tourists, this small center is a fine example of 'wilderness architecture' by noted park architect Herbert Maier. — Lonely Planet

Mammoth's visitor center explores the park’s early history and formation, including the role the army played in protecting Yellowstone from poachers and vandals. Rangers give talks several times a day. — Lonely Planet