More of a fortlet really, worth a visit more for the view and the ambience, than for any great remains. I visited here in summer 1994, and (assuming the intervening years have been kind) the remains of the fort are still covered with trees, and the ramparts are still visible in places. The area was littered with stones that may have been bits of the fort. It definitely affords excellent views over the sands, with the southern lakes hovering in the background.
If you go to visit the three brothers,
( themodernantiquarian.com/site/80 )
the fort is easily reached from the bridleway, through Strickland Wood. However the path involves rough woodland surfaces, not suitable for those of limited mobility. The area is a nature reserve, noted for it’s unusual lepidoptera, so tread extra careful.