Hoyos del Feo

From the mooring you head west and pick up a ravine in the lava that gradually gets deeper as you follow it. It is a straightforward line to swim: the ravine does the navigating, so you can spend your attention on the walls either side of it rather than on your compass. Watch your depth building steadily rather than in steps, because the ground never levels out for long on the way out.

The ravine ends at a vertical wall with a small cave just beyond 30 meters, and that is the turn of the dive. Alongside the drop-off the seabed is fairly light-coloured sand, so the base of the wall is bright and the shape of the face stands out against it. Look, then turn: at this depth there is no reason to linger past your plan.

The way back is the ravine again in reverse, shallowing steadily as you go, which puts the whole ascent over terrain rather than out in open water and makes the gas plan simple: deepest at the far end, shallower every minute after it. Follow the ravine east until the mooring comes back into view, finish over the lighter ground near the buoy, and hang the safety stop on the line.