Should we rule out fake 19th century castles, & manor houses which were crenellated as status symbols, after castles ceased to be of much military significance?
No truly local castle here, there being nothing to see on Castle Hill except 19th century & later houses. There's a small motte in the abbey grounds, & there was once some kind of fortification on it (probably wooden), but it only lasted 30 years or so, until the end of The Anarchy.
Plenty within a bike ride, though. I'll have to dig out my pictures of Wallingford: a few ruins & some impressive earthworks.