Appalachian Trail

The Appalachian Trail is the original American thru-hike — 3,540 km from Springer Mountain in northern Georgia to the summit of Mt. Katahdin in central Maine, passing through 14 states along the spine of the Appalachian Mountains. Conceived by forester Benton MacKaye in 1921 and completed in 1937, it predates the Pacific Crest Trail by decades and remains the most-walked long-distance trail in the United States — around 3,000 thru-hike attempts each year, with about 25 % finishing.

The trail's character is unlike its western counterparts. Where the PCT is high, dry, and exposed, the AT is forested, humid, and rooted — known affectionately as "the green tunnel" for the canopy that covers most of its length. Climbs are short but constant; thru-hikers gain an average of 215 m per kilometre, the equivalent of climbing Everest 16 times over the course of a thru-hike. The trail crosses cultural regions more than climate ones: the Smoky Mountains in Tennessee and North Carolina, the long Virginia ridge, the rocky Mid-Atlantic, New England's classic White Mountains (with the dangerous Presidential Range), and the 100-mile Wilderness in Maine before the final climb up Mt. Katahdin. Mt. Washington in New Hampshire, at km 3,140, has some of the world's worst recorded weather — winds over 370 km/h have been recorded on the summit.

The AT requires no permit beyond a Smoky Mountain backcountry permit ($40) and a Baxter State Park entry. The network of 200+ three-sided trail shelters is the AT's signature feature — built and maintained by trail clubs, free to use, and the social backbone of the trail. Resupply is easy by long-trail standards — towns are 3–7 days apart for most of the trail. Most NOBO thru-hikers start at Springer Mountain in mid-March and finish at Katahdin in September or October, before Baxter closes for winter. The total cost typically runs $5,000–8,000 across the 5–7 months on trail.