Worthing is good for natural. Some complain that it isn't "real" natural because it's sea defence rocks. Honestly, who gives a shit, rocks are rocks. There's also some new ones about 10/15 minutes ride down shore, which none of us have actually riden yet, so i can't tell you about them. Had a few million spent though, apparently, so can't be too bad. Brighton has a bit too. If you go to preston park, there is a big hilly garden type place opposite, and if you go in there and walk up a bit, there's lots of rocks there, but with the tree's and moss, some are a bit sketchy, but it's ok if you also ride the rest of brighton, as you couldn't spend all day there.