Indigo Tunnel is an abandoned railroad tunnel in Allegany County, Maryland, located about 1 mile (1.6 km) east of Little Orleans. Built by the Western Maryland Railway (WM) in 1904 as part of its Cumberland Extension project from Hagerstown west to Cumberland along the Potomac River valley, which involved construction of four additional tunnels and 23 bridges, Indigo was the WM's longest tunnel. The new rail line opened in 1906. Trains ran through the tunnel until the rail line was abandoned by the newly formed Chessie System in 1975, in favor of the parallel Baltimore and Ohio railroad line on the opposite side of the Potomac River.
