Associated with the Penshaw Monument is the tale of the Lampton Worm, which is apparently how the hill got its rings, indeed this type of hill fort would be highly unusual, even in the period in which it was built few such ornate hill forts existed for hundred’s of miles.
See the website for the full text.
Uh, no - the original locale associated with the Lambton [not Lampton] Worm is actually Worm Hill and nearby Worm Well, both the other side of the River Wear, at Fatfield.
It was only later moved to Penshaw Hill, presumably because it's now such landmark, thanks to the monument.