Ynys y Pandy is an impressive, three-storied slate mill standing beside a lane, off the A487, that leads to Llyn Cwmystradlyn Reservoir. Built in 1855 to serve the Gorseddau quarry, the ruin has arched windows and is reminiscent of a ruined abbey or cotton mill. It is unusual because most slate mills had only one floor. However, the venture was not a success and the mill closed after a few years. The huge pit for the waterwheel is the main internal feature. It is now an ancient monument.