From Praia do Prainha (long beach of Alvor) or Praia dos Tres Irmaos, take the stairs to the top of the cliff and follow to the east the marked trail. This trail did not goes close to the cliff. You have to found by yourshelf (after bypassed some private houses) a parallel unmaintained path which give access to some secluded creeks and natural sea arches. The first one harbor a large sinkhole with a pierced cavity open on the ocean. It is considered like an old sinkhole because the circular partition was already strongly eroded.