The day opens on a blue so clean it seems to have been filtered: sunlight cuts across the Tagus as the van slips out of Lisbon, and by the time you crest the low ridge of Arrábida the Atlantic has stripped itself to cobalt. You step off at a quiet cove—rocks rimmed with green, a small fisherman’s village where nets sag in the sun—and the sea is inviting and sharp. Guides hand out masks and fins; the shoreline hums with tiny life. Underwater, bream and damselfish move like punctuation marks through beds of seagrass. On land, limestone cliffs angle down to hidden beaches and vineyards press into the slopes above, as if the mountain itself were farming the sea.