Perched on gran­ite cliffs near the Por­tuguese roy­al retreat of Sin­tra, the vil­lage of Azen­has do Mar is the site of a tru­ly awe-inspir­ing ocean pool. At high tide, it’s com­plete­ly filled up by mas­sive Atlantic waves. As the water grad­u­al­ly ebbs away, the pool remains as a patch of still water, fringed by a sandy beach.