Benagil is a sea cave on the Algarve coast of Portugal with a round hole in its roof and a crescent of golden sand underneath that no path reaches. The cliffs along this coast are soft limestone, hollowed through by the sea into caves and arches. Benagil is the one that also gave way from above, so its dome opens to the sky with two sea arches at its foot. The hole decides the hour. Only between late spring and early autumn does the sun stand steep enough to drop a hard-edged column of light through it, and only around the middle of the day, for a few minutes. The rest of the year the light comes in sideways through the arches instead. Nobody sets foot on the sand any more. The cave is seen from the water, from a boat with its engine cut or from a kayak, while the column slides across the beach as you turn.
The village outside is about sixty people, and it fished the ocean until late last century. The boats still launch straight off the sand, reversing their hulls into the surf, but they run a few hundred metres east now and are back within the hour. On either side of the cave the same limestone makes small coves and arches over clear green water where you can swim as much as you like, from Benagil's own beach or from Praia da Marinha next door. The better way to understand the place is from the top. A trail climbs out of the village onto a clifftop that is hollow underneath, past shafts in the rock fenced off at the rim — algares, the Portuguese call them. At some the roof has gone completely, so you stand at the edge and look down into moving green water. Benagil's own skylight is one of these. The path is called the Seven Hanging Valleys, and that is exactly what they are: stream valleys that now stop in mid-air, cut off when the cliff retreated out from under them.