The Best Time to Visit Vatnshellir Lava Cave

The whole year in one table

Temperature, rain and wind below are five-year means measured at the cave's own coordinates rather than at Reykjavík, which sits in a milder, more sheltered spot two hours away.

Reading it

The pattern is not the one people expect. Rain barely varies: every month here gets between 135 and 205 mm, and September is the wettest of the year rather than any winter month. What actually swings is wind, and wind is what closes the road and makes the ten minutes at the hatch unpleasant.

So the shoulder months win on the metric that matters. September has autumn's light with summer's departure frequency and none of July's queue.

What you get

Mean air temperature at the cave reaches 10.0°C in July and 10.1°C in August, the calmest wind of the year at 20 to 21 km/h, and daylight that stops being a constraint at all. Around the summer solstice this latitude gets about 21.7 hours of it, which means a 21:00 departure is still a daylight drive home.

Departures run roughly hourly between 10:00 and 18:00. That is four times what winter offers and it is the practical argument for coming now.

• Warmest and calmest month of the year above ground
• Most departures, so the most chance of a slot that fits your day
• Route 574 reliably open
• August is the wettest of the three at about 201 mm

The cost

Group size is capped by the width of the staircase, and in July and August departures fill by mid-morning. Turning up at the car park at 14:00 in August without a booking is how people end up driving four hours for nothing.

The car park holds about fifteen cars and it overflows. And the peninsula is at its busiest, so Djúpalónssandur and Lóndrangar, which are the reason to be on this road at all, come with coaches. If you are here in high summer, take the first departure of the day and see everything else before ten.

Why September wins

Mid-September still gives about 13.1 hours of daylight, which is more than enough for a Reykjavík day trip with three stops on it. Mean temperature is 7.0°C, wind is up only slightly at 25 km/h, and the summer departure pattern has not yet collapsed.

What has collapsed is the queue. The coaches thin out after the third week of August and the car park stops being a problem. On a mid-September weekday I have had a four-person group, which changes the tour: you can ask questions, you can stop where you want, and you can get the photograph of the staircase from below that a full group makes impossible.

• About 13.1 hours of daylight in mid-September, 9.7 by mid-October
• 7.0°C mean in September, 4.0°C in October
• The wettest stretch of the year at about 205 mm in September
• Small groups, and the tour is better for it

October's trade

By mid-October you are down to 9.7 hours of daylight, which still comfortably covers a day trip but starts to force choices about how many stops you make. Departures begin thinning towards the winter pattern. The upside is that the moss on the lava field goes from green to rust, and the cave entrance photographs better in October than in any other month.

The cave does not notice

This is the point everyone misses. Vatnshellir has no closed season. The temperature 35 metres down is the same in February as in July, there is no ice to form or melt, and nothing about the route changes. Compare that with Iceland's glacier ice caves, which are a winter-only product because they melt, or Þríhnúkagígur, which only operates from roughly May to October.

What changes is everything above the hatch. Mean air temperature at the cave sits at -1.0°C in December and -0.9°C in January. Wind averages 27 to 30 km/h. And daylight drops hard: about 6.3 hours in mid-November, 5.2 in mid-January, and about 3.7 around the solstice.

• Two or three departures a day, so your date is chosen for you
• About 3.7 hours of daylight at the solstice: the drive out and back is in the dark
• -1°C mean and 30 km/h wind on an exposed lava field
• Empty. On some winter departures the group is four people

Making a winter visit work

Take the first departure of the day, because it is the only one with light on both sides of it. A 45-minute tour fits inside a December daylight window with room for one other stop, and Lóndrangar is five minutes away.

The northern-lights argument is real but do not overweight it: you are on the peninsula for the cave and the coast, and the aurora is a bonus you cannot book. What you can book is a departure you are able to cancel free up to 24 hours before, which is the only sensible way to handle an Icelandic winter forecast.

Underrated

April sits at 2.4°C mean and May at 5.2°C, with wind back down to 22 to 23 km/h and the daylight climbing fast. By mid-May this latitude has about 18.6 hours of it, which is effectively unlimited for a day trip.

Departures build back towards the summer pattern through May. Crowds do not arrive until late June. If September is taken, this is the next best window, and May in particular gives you summer's light and autumn's emptiness.

The one thing spring does not give you is settled weather. April can hand you sleet on Route 574 with no notice.

Month by month, in brief

Daylight is measured at the cave's own latitude; temperature and wind are five-year means at its coordinates.

Three variables, none of them the cave

This is the counterintuitive part, and it is worth stating plainly because most seasonal guides get it backwards.

First: the cave is a constant. Nothing about the underground experience varies by month.

Second: wind, not snow, is what stops you. Route 574 is paved the whole way around the tip of the peninsula, and it crosses open lava with nothing to break a westerly. Vegagerðin restricts or closes it on wind far more often than on snow, and it publishes live status at road.is. Check it the morning you drive, not the week before.

Third: daylight decides how much of the peninsula you see, not whether you see the cave. The tour is 45 minutes and the car park is lit by your headlights if it comes to that. What you lose in December is Lóndrangar, Djúpalónssandur and the coast, which is most of the reason to drive out here. Everything within 25 minutes of the car park is what the daylight budget is actually for.

Rain is not the variable you think

Every month here gets between 135 mm and 205 mm. September is the wettest of the twelve and December the driest, which is the opposite of what most visitors assume. Rain does not affect a cave tour at all, and it barely affects the drive.

Plan around wind and light instead.

First departure, in every season

In summer, the first departure of the day is the one with space, the smallest group and an empty car park, and it leaves the rest of a long day for the coast.

In winter, the first departure is the only one that guarantees you daylight for the drive at both ends.

The cave itself does not care what time it is, which is one of the few genuine advantages of an activity with no sky in it. If you only have one slot available, take it; there is no bad hour down there.

The cave stays open; the road might not

Rain, sleet and cold do not cancel this tour. What cancels it is Route 574 closing, or you deciding not to drive a wind-battered road across open lava, which is a legitimate call.

Cancelling is free up to 24 hours before departure and nothing is charged when you reserve, so the winter pattern that works is to book two or three days out once a forecast exists rather than three weeks out on hope. If the road shuts on the morning, your guide is not getting there either.