What makes Praia da Falésia worth singling out is not a wreck or a legend but a wall, and the wall is a clock. For close to six kilometres the cliff behind the sand stands cut in horizontal bands, and those bands are not decoration. They are two stacked geological formations and the boundary between them, exposed in cross-section by the Atlantic, recording on the order of five million years of deposition. At Açoteias you can walk to the base of it and read the whole column top to bottom.

The two formations. The lower, paler unit, greyish-white shading to cream, is the Falésia Sands, deposited in a deltaic system during the Pliocene. The upper unit, the part that gives the whole beach its colour, is the Quarteira Sands, accumulated on a shallow continental shelf from the Upper Pliocene into the Early-to-Middle Pleistocene. The red and terracotta of that upper band is iron oxide, the same chemistry that reddens rust and Martian soil, staining the old shelf sands. Between the two sits an intermediate series of fossil-bearing deposits that marks the Pliocene-Pleistocene boundary, so the cliff carries not just two layers but the seam where one geological epoch gives way to the next.

What is inside the seam. That intermediate band is not empty. It holds a roughly half-metre fossiliferous conglomerate with the teeth of large sharks, Isurus and Otodus megalodon among them, alongside marine-mammal remains, the residue of a warm shallow sea. Higher in the sequence, near the top, a two-metre siltstone unit shot through with root structures is read as a paleosol, an ancient land surface, dated to roughly 125,000 years ago. So the column does not only stack sand on sand; it runs from open-shelf marine deposits through a fossil seam to a buried soil, a legible change of environment over deep time held in a single roadside cliff.

Why the bands are red, white and falling. The cliff is soft. It is sand and clay, not hard rock, and it behaves accordingly. Winter rain does not weather it slowly; it carves grooves and gullies straight down the faces, and slabs and aprons of material slump to the base. That collapsing sediment is exactly what feeds the beach: the wide pale strand below is the cliff coming apart and being spread out by the sea. The legibility of the bands and the instability of the cliff are the same fact. You can see five million years of stratigraphy precisely because the Atlantic keeps shaving the face clean, and the face keeps shaving because it is too soft to hold.

Why Açoteias, specifically. Falésia runs from the fishing district of Olhos de Água in the west to Vilamoura in the east, and the western half, the Açoteias reach near Olhos de Água, carries the tallest and most dramatic cliffs, rising to something like 30 to 40 metres. It is also the access-managed end, reached down steps and boardwalks from resort car parks, which is the honest trade: the most legible, most photographed section of the wall is also the busiest and the most built-up behind. The pine crowning the red is the umbrella pine the Pine Cliffs resort is named for. Stand at the base in the last hour of light, when the low sun saturates the iron-oxide red and throws the pine into near-black silhouette, and the cliff reads as what it is, a five-million-year section of the Algarve coast standing on end, dissolving as you watch it.