Trecastell is a zinc and lead mine which was worked intermittently from the 1750s (possibly much earlier) until 1955. A public road crosses the sett. To the west of the road were the earlier upper workings accessed from three hillside adits. To the east of the road were the much larger lower workings following several lodes, with stoping extending to a depth of 105 fathoms and accessed primarily via shafts. The lower workings have now been "landscaped" and the ground choked with birch saplings and gorse, and very little of the site's industrial past can be seen.
For more details see Mines of the Gwydyr Forest Part 7, J Bennett and RW Vernon, Gwydyr Mines Publications, 1997