The 26-year-old woman was attacked in the Hothampton Sunken Gardens, Waterloo Square, Bognor, at about 02:00 BST on Saturday.
Sussex Police said a 42-year-old man from Bognor was arrested on suspicion of rape on Saturday evening.
Det Sgt Alan Fenn said the force was "not looking for anyone else in connection with this rape."
A man has been arrested on suspicion of raping a woman who was subjected to a "prolonged assault" in West Sussex.