The Doon, or Drumadoon Hill Fort, is an Iron Age fort north of Blackwaterfoot on the Isle of Arran. The hill fort used the high cliffs on the seaward side for protection against an attack by water and a built wall on the other three sides against threats from the land side. The wall measures up to 3m thick and encircles the entire summit of the headland. The Doon is 170m at its widest and is therefore the largest fort on Arran. The remains of the wall on the top is covered by turf and hard to see today, but the steep cliffs on the west show the fort's strategic location.