This year marks the 100th anniversary of what novelist and environmentalist Wallace Stegner called "the best idea we ever had," the founding of the National Park Service. The greatest hits - Yellowstone, Yosemite, and the Grand Canyon - attract carloads by the millions, but many parks can be visited in absolute solitude. Often, a smaller park or historic sight boasts a powerful but little-known story about America's heritage. Here are a few of our favorites:

Theodore Roosevelt Inaugural National Historic Site, Buffalo. After President William McKinley was assassinated in Buffalo in 1901, Vice President Theodore Roosevelt rushed to the city, where he took the oath of office in this house. It's one of the few inauguration sites outside Washington, and it provides a fascinating history of the turn of the 20th century.

Moores Creek National Battlefield, Currie, N.C. The three-minute skirmish fought on Feb. 27, 1776, known as the battle of Moores Creek Bridge, was a major, and surprising, British defeat. Less than two months later, North Carolina instructed its delegates in Philadelphia to vote for independence - the first colony to take that bold stance. The parkland looks much as it would have in 1776 during this pivotal moment in American history.

Dry Tortugas National Park, Key West, Fla. A tiny islet 70 miles west of Key West is home to the colossal 19th-century Fort Jefferson. Visitors are scarce, as the only access is via boat or seaplane. In addition to an idyllic setting amid crystal-clear water, it's where Dr. Samuel Mudd, who set John Wilkes Booth's broken leg after the assassination of President Abraham Lincoln, was imprisoned.

Tonto National Monument, Roosevelt, Ariz. Cliff dwellings built by the Salado Indians in the 14th century await visitors who tackle the half-mile trail winding through a forest of saguaro cacti in the Sonoran Desert. Despite its setting 100 miles east of Phoenix and only four hours south of the heavily visited Grand Canyon, this intriguing site that offers history and stunning scenery is never crowded.

There are more than 400 sites in the National Park Service. This summer, celebrate the organization's centenary by exploring a few that are lesser known. For more information, go to By the way, America's smallest national park, measuring only .02 of an acre, is the Thaddeus Kosciuszko National Memorial, at 301 Pine St. in Philadelphia.

Larissa and Michael Milne are the authors of "Philadelphia Liberty Trail," a guidebook to the city's historic district.