The Merritton Tunnel, also known as the Blue Ghost Tunnel and the Grand Trunk Railway Tunnel, is an abandoned railway tunnel that connected Merritton (now part of St. Catharines) and Thorold, Ontario. The decision to build the tunnel came from the need for "a more durable and less interrupted way to cross the new canal" situated directly above it via vehicles. Built in 1876, the tunnel is located between locks 18 and 19 of the former third Welland Canal, was built using Queenston limestone and spans a total length of 713 feet when including the winged stone work at either end. Hundreds of men armed with picks and shovels, as well as several horses were used in the excavation of the tunnel. The tunnel was used periodically until 1915, when Harry Eastwood was the last official engineer to pi