Looking for adventure? Challenges, education, and exploration await at our country's 401 national parks— 84 million acres' worth in every single state across the U.S.! Here are the country's three most-visited National Park Service sites and reasons why you should visit:

1) Great Smoky Mountains National Park: 9,354,695 visitors in 2013
Straddling the North Carolina-Tennessee border, the Great Smoky Mountains National Park offers 800 spectacular miles of trails over 521,490 acres. In addition to hiking, visitors can camp, picnic, bicycle, explore historical sites, or fish the park's 700 miles of streams. (See a full list of to-dos here.) Watch your step: A trip to this national park might put you within range of a black bear, elk, or white-tailed deer.

2) Blue Ridge Parkway: 12,877,368 visitors in 2013
Awe-inspiring mountain passes are the hallmark of the Blue Ridge Parkway, a scenic 469-mile drive that connects Virginia's Shenandoah National Park with North Carolina's Great Smoky Mountains National Park. A good old-fashioned road trip along the Parkway promises pit stops way better than your standard fuel-up: Expect scenic overlooks, hiking trails that lead to secluded waterfalls, and plenty of native flora and fauna. Check out suggested itineraries here.

3) Golden Gate National Recreation Area: 14,289,121 visitors in 2013
America's most visited national park site, the Golden Gate National Recreation Area comprises 24 attractions in and around San Francisco, California. These include Alcatraz, the Muir Woods redwoods forest, and of course, the Golden Gate Bridge. Read more about the Golden Gate National Recreation Area here.

Ten Most Visited Parks [National Parks Conservation Association]

CC-BY-SA-2.0/Flickr/Salim Virji