Hálsanefshellir, the basalt cave

At the eastern end of Reynisfjara the cliff opens into Hálsanefshellir, a shallow sea cave whose ceiling is a mass of hexagonal basalt column ends, like a honeycomb turned to stone. From inside, the mouth of the cave frames the black beach, the surf and the Reynisdrangar stacks out at sea, and the whole thing reads as a single dark geometry with two people standing in it.

The craft is exposure. Facing out, the beach is many stops brighter than the cave, so your photographer will either silhouette the couple against the opening or bring flash to hold both — both versions are strong and it is worth agreeing which you want beforehand. Overcast days narrow the gap and are genuinely easier. Turn the other way and the columns themselves become the subject: a couple standing against the stacked hexagons, with a wide lens looking up.

Now the part that is not optional. Reynisfjara produces sneaker waves — waves several times larger than the ones before them, running far up a beach that gives no warning — and people have been killed here, including in front of everyone else on the beach. The cave sits close to the water: the sea reaches the cave mouth on some tides and in some swells, and the entrance area can be cut off. Check the beach's official warning system and the swell forecast before you go, never turn your back on the water, keep everyone above the highest wet line by a wide margin, and abandon the frame rather than the safety distance. Falling rock from the cliff above is a second, quieter reason not to linger under the overhang.

Practicalities: the walk from the car park is five to ten minutes over sand and rounded stones that roll underfoot, awkward in heels. There is no shelter and the wind here is often severe. Come at first light for an empty beach; by mid-morning the cave has a queue of people photographing it one at a time.