Harecastle Tunnel is technically two tunnels, with just one navigable today. They are located side-by-side on the Trent & Mersey Canal in Kidsgrove, north of Stoke-on-Trent. Both are nearly 3000 yards in length. The first Harecastle Tunnel, engineered by James Brindley, took a total of eleven years to construct. When it was completed in 1777 it was more than twice the length of any other tunnel in the world at that time.

The second tunnel, built by Thomas Telford, was needed to increase capacity and took just three years to complete. When it was opened in 1827, Telford could benefit from advancing knowledge of tunnel engineeting and was able to excavate a much wider tunnel, allowing a towpath for horses (the Brindley tunnel required boatmen to 'leg' their boats through).

To construct the canal, Brindley set the the tunnel line of the tunnel over the hill and then sunk fifteen vertical shafts into the ground from which the bore was dug. The changing rock type ranged from soft earth to Millstone Grit and regular flooding caused enormous difficulties, the latter resolved by steam driven pumps and large stoves.

Without a towpath it could take up to three hours to get through the tunnel. The tunnel was 3.7 m (12 ft) tall at its tallest point and was 2.7 m (9 ft) feet wide at its widest, which proved subsequently to be too small. After subsidence in the early 20th century, due to nearby mining operations, it was closed after a partial collapse in 1914. Inspections of the disused tunnel continued until the 1960s, but since that time, there has been no attempt to investigate the interior of the tunnel at any significant distance from the portals.

The gated portals can still be seen from the canal, although it is no longer possible to approach the mouth of the tunnel in a boat. In recent times, water entering the canal from the Brindley tunnel has been blamed for much of the prominent iron ore (responsible for the rusty colour of the water) in the canal, and there are proposals to install filtering (possibly using reed beds) at the northern portal.

After completion of the Telford tunnel, both bores were used, running one-way traffic in opposite directions. Though the Telford tunnel remains open, it too suffers from subsidence: the towpath has been removed, and headroom is in places considerably reduced. Between 1914 and 1954 an electric tug powered from an overhead wire inside the tunnel pulled boats through. Since the tunnel was not designed for use by diesel-powered boats, there are no ventilation shafts and an air extraction fan-house has been built around the portal at the southern end . Unless a boat is actually passing the portal, airtight gates are closed, allowing the fan system to extract more efficiently.

The map above pinpoints the North Portal.