Depending on the trains, may be a bit more than an hour, but Arundel is wonderful. The castle is the oldest inhabited castle in England after Windsor; the keep dates to the Norman Conquest. The gardens are lovely and the surrounding fields are worth walking around. They used to have mock jousting tournaments on the August bank holiday weekend.
There’s a small lake you can row in. The town itself is very pretty, with antique places and old-fashioned sweets shops with parma violets and sugar mice.