Tafoni
Tafoni, the swiss-cheese-like formation visible in the above image forms through a combination of chemical salt weathering and cyclic wet/dry periods. Tafoni is most commonly found in desert sandstones cemented together with calcium carbonate, or near bodies of salt water.
Tafoni in the above case is formed through the intrusion of saltwater into porous sandstone, which, when the water evaporates, fills pore spaces with precipitated out halite (salt). The salt crystals expand enough to dislodge grains of sand from the rock, which are then blown or washed away, leaving a small hollow in the rock. Over time that hollow expands, and you're left with the same distinct tafoni structure on the surface of the rock.
This is not the only way in which tafonit can form. In more arid environments the process goes more like this: Water wicks through the porous sandstone, dissolving CaCO3 into its constituent ions, which precipitate out on the surface of the rock as the water evaporates. This leaves ridges of CaCO3 and unconsolidated sand particles on the surface of the rock. The sand is blown or washed away, and the rock is left with distinct round pockmarks in a honeycomb pattern covering it.