The Appalachian Trail, or AT, stretches more than 2,000 miles along the US East Coast.
The longest marked trail in the country runs from Georgia to Maine. It connects 14 states and passes through ridges and valleys of the Appalachian mountain range.
Parts of the AT are within a couple hours drive for millions of Americans, but few have walked its full length. Each year, thousands of people attempt to hike the entire AT. Only one in four succeeds.
National Geographic explored the wooded footpath, travelling south to north, in a 50-minute documentary. You can take the adventure in our slideshow or watch the movie on Netflix.
The Appalachian Trail, better known as the AT, stretches about 2,175 miles along the eastern United States.
It runs from Georgia to Maine, making it the longest marked trail in the country, and one of the longest in the world.
The AT is divided into four sections: The Southern Mountains, The Virginia Highlands, the Mid-Atlantic Lowlands, and New England.
The AT was first proposed in 1921 by Benton MacKaye, a former forester and newspaper editor. He hoped the trail would be a way for people to escape city life and reconnect with wilderness.
This was largely the work of volunteers who found routes, made maps, and established local trail clubs.
Even today, the AT is maintained by thousands of volunteers who clean the trail, clear fallen trees, touch up trail markers, and warn hikers of hazards.
Someone who aims to hike the whole trail in one shot is known as a 'thru-hiker.' 'Day-hikers' or 'section-hikers' do small portions of the trail.
Every year, around 2,000 hikers attempt to tackle the AT's full length (around 2 to 3 million people walk a portion of the Trail).
There are two kinds of thru-hikers: Northbound (Georgia to Maine) and Southbound (Maine to Georgia). Most thru-hikers walk north, starting in Georgia in March or April and finishing in Maine in September.
Some hikers load up on food high in calories like Snickers bars to maintain strength. Many climbers can burn up to 6,000 calories a day.
Fewer than 1,000 people have completed the AT southbound, in part because it's a tougher hike that starts with Mount Katahdin, the hardest climb of the entire path.
If you start in the Southern Mountains, the trail head begins at the top of Springer Mountain in Georgia.
The trail head is 10 miles from the nearest access road. A crew of volunteers helps to shuttle hikers to the starting line.
Chad Kinsey, a 33-year-old network administrator, is being dropped off today. Kinsey is a section-hiker, hiking for five to seven days at a time.
Extra food, tents, and water bottles either get dumped or traded in for lighter versions at the store. Many ambitious hikers think they are going to read at night, but end up being too tired, so lots of books are also cast away.
Along the way, he passes one of the oldest hiking shelters on the Trail, built in 1934. There are more than 250 shelters along the Trail. These are often three-sided structures with a wooden floor, also known as lean-tos.
Kinsey's journey ends on the top of Blood mountain, the highest peak on the Georgian section of the AT.
More than 70 miles of Trail weaves through the Great Smoky Mountains National Park, the most visited national park in America.
Next, hikers will tackle the Virginia Highlands. Compared to the Southern mountains, this patch of the trail is relatively flat and hikers can cover 20 to 25 miles per day.
Backpackers have been on the trail for about a month when they reach the trail town of Damascus, Virginia at the southern border.
More than one-fourth of the AT (about 550 miles) slices through Virginia. Moving north, 105 miles of this section cuts through the heart of Shenandoah National Park.
The black bear is one of the largest animals that lives around the trail. They are especially common in Shenandoah National Park.
Hidden cameras have snapped more than 5,000 images of creatures roaming near the AT, including the bobcat seen here.
Venomous snakes including the Rattlesnake and Copperhead are common along rockier sections of the trail.
Surprisingly, the biggest danger does not come from bears or snakes, but from ticks that carry Lyme disease.
Thru-hikers hit the half-way point at Harper's Ferry, West Virginia, which also marks the end of the Virginia Highlands portion.
The Mid-Atlantic section of the trail takes hikers through Maryland and Pennsylvania. This is one of the more travelled portions, where the Trail hugs farmlands and often crosses roads.
The lowest elevation of the hike comes when the AT crosses the Hudson River at Bear Mountain Bridge.
Northbound thru-hikers hit New England in the fall. At this point, 80% of the trail is behind them, but one of the toughest sections still lies ahead.
Through New Hampshire and Maine, the path is rugged, steep, and slippery. Maine's 281 miles of trail are some of the most strenuous and remote to hike in all 14 states.
Gary Hill has been on the trail for six months and is three days from the northern terminus on Mount Katahdin. He is 70 years old.
Gary also faces the risk of getting kicked off the trail before he reaches the end. The trail up Katahdin is closed on days when weather makes hiking there dangerous.
When Gary wakes up, the weather is good and he begins his five-hour trek to Baxter Peak on Katahdin.
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