at Todd's End Field, on which work started in 2015. The complex, known as "The Portal", was formally opened by Princess Anne on 4 March 2016. Blowers Green Pumphouse is still used for social functions and storage. Route The earliest part of tunnel system was built to help with the transport of limestone extracted from the mines inside Castle Hill through which the tunnel runs. This was Lord Ward's tunnel, which leads to Castle Mill Basin. From there the main tunnel runs, via the Cathedral Arch, to Parkhead, near Netherton. At Cathedral Arch a branch canal led into the Little Tess Cavern mine workings. This route is now blocked, but has been by-passed by two new tunnels. The southern end, including the southern portal, of the tunnel had to be rebuilt in 1884 due to subsidence caused by adjacent coal mines. This section of the tunnel was built several feet wider than the original tunnel bore. The southern portal bears a brick date stone of 1884. Another canal tunnel at Castle Mill Basin, now blocked off by a dam, leads under Wren's Nest to two underground basins, east basin and west basin, and was used to transport limestone from the underground mine workings. Surface quarries were also opened; they outlasted the underground workings and were last used in the early 1920s. The land above the underground workings, together with the surface quarries, became a National Nature Reserve. Dudley Tunnel today The restrictive dimensions of the tunnel and the absence of a towpath mean that many boats are unable to pass through it. Those that can are not allowed to use diesel engines due to the lack of ventilation in the tunnel. Visitors may take a battery-powered narrowboat trip operated by Dudley Canal Trust either through the tunnel or partway through the tunnel and the adjacent mines; and, also, try legging the boat. The rock of Castle Hill into which the tunnel is dug, oolitic limestone, allows visitors to see trilobite fossils preserved within it. Some fossils which were considered notable and were located close to the waterline, have been removed to prevent them from being eroded and attacked by visitors. Other parts of the tunnel pass through a dolerite known locally as Rowley Rag; and through Coal Measures rocks. Coordinates (With links to map and aerial photo sources) See also Lapal Tunnel Legging (canals) List of canal tunnels in Great