The Standedge Tunnels are four parallel tunnels that run beneath the Pennine Hills between Marsden and Diggle in the north of England. There are three railway tunnels and a canal tunnel which opened in 1811 and is part of the Huddersfield Narrow Canal. All four tunnels are linked by cross-tunnels which allowed the railway tunnels to be built much more quickly by allowing 'waste spoil' to be removed by boat and reduced the need for shafts during the construction. Standedge Canal Tunnel is the longest, deepest and highest canal tunnel in Britain. It is 16,499 feet (5,029 m) long, 636 feet (194 m) underground at the deepest point, and 643 feet (196 m) above sea level. The canal tunnel, closed in 1943, was the beneficiary of a £5 million restoration project in an effort to re-open the entire Huddersfield Canal. Several rock-lined parts of the tunnel were stabilised by rock bolts, or where impractical, concrete was used to stabilise the rock face. The tunnel re-opened in May 2001 but it was felt unsafe for boaters to navigate the tunnel under their own diesel power due to the extreme length of the tunnel and the lack of ventilation. Instead, electric tug boats hauled narrowboats through the tunnel. Since the 2009 season however, boats have been allowed to travel through the tunnel under their own power, with a chaperone on their boat, monitored by a service vehicle through the parallel disused 1848 railway tunnel which can act as an emergency escape route. Of the railway tunnels, only the tunnel built in 1894 is currently used for rail traffic. The Standedge Tunnel Visitor Centre at the Marsden end is a base for boat trips into the canal tunnel and hosts an exhibition. The canal is now entirely used by leisure boaters.