Dating from the 1600s, Plas Machynlleth is an imposing mansion on the edge of the town centre which was a residence of the Marquesses of Londonderry. the 7th Marquess donated the house to the town of Machynlleth. It was converted into the 'Celtica' heritage exhibition in 1998, but this was unsuccessful and it closed in 2006, and is now operated as a corporate and conference venue.