Sandal Castle, Henry VI, part 3 : 1, 2

The castle's remains (although not much is remaining) are still there at Sandal, Wakefield:

Latitude: 53:39:31N Longitude: 1:29:25W

The field of battle in scenes 3 and 4 refers to the Battle of Wakefield, which took place on Wakefield Green to the west of Sandal Castle.