When walking near the town of Tenextepec, Veracruz, Esme and I found a wall of sand with nice ridges created by erosion, and some tiny "caves".
In the above photo it almost looks like one can walk inside the big cave and explore its depths. In reality, the "cave" was just about 30 cm heigh. In my opinion, the next photo of cactuses shows a similar effect. Coincidentally it was taken on the same day.