Deildartunguhver

The steam is visible from a long way off, a white column standing over the floor of the valley. Up close the water surges out of a line of vents and mineral terraces, boiling and loud. The ground around the springs is green and overgrown, warmed from below while the rest of the valley stays cold. The air smells of hydrogen sulphide, and the steam drifts across the platforms. One plant here is found nowhere else: Struthiopteris fallax, the only fern endemic to Iceland, grows in the warm ground at Deildartunguhver and nowhere else in the world.

• Smell: the air carries hydrogen sulphide, the rotten-egg smell of geothermal water. The steam drifts over the platforms and fogs camera lenses.
• A short stop: this is a viewing site and nothing more. Once you have walked the platforms, there is nothing else to do here.
• Food is not certain: a greenhouse beside the spring sells hot dogs and other food, but it is not always open.
• Next door: the Krauma spa stands right beside the spring. The spring itself is for looking at, not for bathing.
• Facilities: there are toilets on site, and payment by card is accepted.

Deildartunguhver lies in Reykholtsdalur, near Reykholt in West Iceland, and it is reached by road. The car park sits at the site itself, and the viewing platforms are a short walk from it over flat ground.

Better: cold, clear days in autumn and winter, when the contrast between cold air and rising steam is at its strongest.

Avoid: building a long detour around it — this is a stop, not a day out.

The spring runs at the same rate all year, so the weather decides how dramatic it looks, not the season.