Recommend parking in layby at bottom just off the road & walking up side of canal. Parking further up is as with all pubs, parking is for patrons only.
Tunnel Facts The length of Sapperton Tunnel is 3,490m (3,817 yards, 173.5 chains or 2.17 miles) and was completed on 28 April 1789. The nominal width is 4.4m (14ft 4in) with a minimum height of 4.7m (15ft 4in). The roof can be significantly higher in parts of the unlined sections, due to the amount of rock that fell during construction blasting operations. The Daneway entrance to the tunnel is 7.5 route miles (12km) from the start of the Thames & Severn Canal at Wallbridge in Stroud. The tunnel is on the summit (highest level) of the canal which is about 111m (360ft) above sea level, and has climbed 73.5m (241ft) from Wallbridge in Stroud. The maximum height of the tunnel overburden (ground between the tunnel roof and the surface level above) is about 66m (216ft)
Tunnel Construction Tunnel construction started in late 1783 and was completed in 1789. The work involved several different contractors. Work began by setting-out the tunnel route on the ground. A number of vertical shafts were then dug along the route to the required depth. Tunnel Shafts The shafts were about 2.4m (8ft) in diameter and it is believed that 26 were sunk in all. The depth of these varied from about 69m (226ft) to less than 10m (32ft). The approximate locations are shown on the tunnel section graphic above. One of the shafts was abandoned before reaching the required depth, probably due to flooding. From the base of each shaft, a 'heading' (small tunnel about 1.2m (4ft) wide and 1.8m (6ft) high) was cut in two directions - along the tunnel line (see picture below). Headings were also cut in from what would become the tunnel entrances. Once headings had been connected, and the alignment checked, the tunnel was excavated to its full size, and lined with brick or stone where required.
Remember you're responsible for your own action. Attempt at your own risk.
Big thanks to Dylan Burgess for pointing out this possible cache location.