Birling Gap is the easiest place to get down to the beach beneath the Seven Sisters cliffs. The National Trust site has a small visitor centre, cafe, shop, and a staircase to the shingle shore, but the real point is the coast: white chalk cliffs, open downland, and long views across the Channel.
It works as a short stop by car or as part of a longer walk. From here you can continue east toward Beachy Head and Eastbourne, or west toward Cuckmere Haven and Seaford. Check tide and cliff conditions before walking along the beach, and keep well back from the cliff edge above.