Length: 14½ km (9.0 miles), or 18¾ km (11.7 miles) with seafront extension. Toughness: 3/10.
09:35 Portsmouth Harbour train from Victoria (Clapham Jct 09:42, East Croydon 09:52), arriving Arundel at 11:04.
Direct return trains from Goring-by-Sea are hourly at xx:27 (to 20:27). You could also take a Brighton train at xx:47 and change at Hove (London-Brighton trains are being diverted via Hove). Arundel and Goring are on different lines but a return to Littlehampton is the same fare and covers both routes.
The start of this walk will be familiar enough from others in the area, but it soon leaves the Arun valley to head east through the Angmering Park estate to a lunch stop at The World's End in Patching. The short afternoon leg includes far-reaching sea views from Highdown Hill and the opportunity to visit Highdown Gardens (free entry), with its fine collection of rare plants and trees.
At Goring-by-Sea station you can decide whether to hop on a train or do the optional loop out to the seafront. If you haven't got an Advance ticket restricting you to a specific train you could even think about strolling along the coast to finish at Worthing or Littlehampton.
You'll need to bring the walk directions from the L=swc.295 , which includes a map of the gardens.