From the rim, Kerið looks as if someone has painted it: red rock, green moss and an aquamarine lake that seems too bright to be real. It isn't painted. The colour comes from minerals in the soil. This ticket gets you in to walk around it and down to the water.

What you'll see at Kerið crater

Kerið formed about 6,500 years ago at the northern end of a row of craters called Tjarnarhólar, part of the Western Volcanic Zone that also takes in the Reykjanes peninsula and Langjökull. The caldera is roughly 55 metres deep, 170 metres wide and 270 metres across, and it's made of distinctive red volcanic rock.

It wasn't created by an explosion. A cone volcano erupted and emptied its magma chamber, and the cone then collapsed into the hollow space underneath. The lake at the bottom is shallow and sits at the level of the water table. Rain doesn't fill it.

Visiting Kerið: good to know

Plan on 30 to 60 minutes. The rim trail is an easy walk, and one of the sloping, moss-covered walls has a path down to the lake. That descent is a moderate gravel path, not a paved ramp. There are toilets on site.

Kerið sits in South Iceland near the usual Golden Circle route, so it's an easy stop to add if you're driving between Þingvellir, Geysir and Gullfoss yourself.

Pro tip: wear sturdy shoes and bring a layer. The weather at the crater changes quickly, and the gravel path down to the lake is steeper and looser than it looks from the top.