The Dover end of the South Downs includes a Norman Castle (phone 0131-421-1067) where you can experience a medieval siege and visit the tunnels used by the military in WWII. The Roman Panted house is open Tues-Sat 10am to 5pm(located on York Street).
On the Eastbourne side of the Downs you can view Beachy Head, the highest of the famous chalk hills know as the Seven Sisters.