The Benagil sea cave is the Algarve's most-photographed natural feature: a vaulted limestone chamber with a sandy floor and a circular hole in the ceiling, accessible only by water. Boat trips from Portimão Marina or Benagil beach run there throughout the day in season, with smaller tours able to enter the cave itself when the swell allows.
The standard tour from Praia da Rocha goes by speedboat or larger excursion vessel along the coast east, passing Praia do Carvoeiro and a series of sea-cave caves before reaching Benagil. Kayak and SUP tours offer a more intimate visit — you can paddle right into the cave and stand on the small beach inside.
Plan for half a day; mornings are calmer and less crowded. Trips do not run when the sea is rough.