The Rail Trail is a massive 3,700-mile bike path being built across 12 U.S. states. Over 55% of the trail is already complete, connecting Washington D.C. to the Pacific Ocean in Washington state. The full trail is expected to take about 75 days to travel, allowing hikers and bikers to visit many historic sites and major cities along the way. Though an exact finish date is unclear, the Rails-to-Trails Conservancy is working to fill the remaining gaps, which they say could take several more decades to complete