Pontcysyllte Aqueduct, Llangollen Canal, Wrexham County Borough, Wales, United Kingdom

Every five years the ends of the aqueduct are closed and a plug in one of the highest spans is opened to drain the canal water into the River Dee below, for inspection and maintenance of the trough.
The canal effectively ends after a short distance on the north side, apart from a feeder to the Horseshoe Falls on the River Dee via Llangollen. The terrain northwards appears to have been the main problem in preventing significant further extension: apart from one or more local spurs of perhaps a thousand yards serving industry south of Cefn Mawr and towards Rhosymedre other traffic was handled by the Ruabon Brook Tramway which climbed towards Acrefair and Plas Bennion, this was eventually upgraded to steam operation and extended towards Rhosllannerchrugog and Wrexham.