Quick summary
- Thrihnukagigur is a volcano with an empty magma chamber; Raufarhólshellir is a lava tunnel formed about 5200 years ago.[1]
- The Raufarhólshellir Lava Tunnel: Underground Expedition takes 1 hour and is led by an English-speaking guide, from US$72.[2]
- Thrihnukagigur day trip is from US$432; Raufarhólshellir by bus is from US$153; basic Raufarhólshellir is from US$68.[3][4][5]
- The Thrihnukagigur lift takes about 6 minutes and the chamber floor measures 50×70 m.[6][7]
- Both tours offer reserve now and pay later and free cancellation up to 24 hours in advance.[2][3]
| Thrihnukagigur | Raufarhólshellir | |
|---|---|---|
| From | from US$432[3] | from US$72[2] |
| Duration | 4 - 6 hours[3] | 1 hour[2] |
| Access | guided hike or helicopter[8] | booked tour with live guide[2] |
| Inside | 35-45 minutes inside[9] | walk a 1360 m lava tube[1] |
| Season | May 5th to October 30th[8] | check availability for times[2] |
"The cave formed as a lava tube during the Leitahraun eruption, which occurred about 5200 years ago. The total length of the tunnel is an impressive 1360 m (4500 ft), the main tunnel being 900 m (3000 ft) long."
Top choice: Raufarhólshellir Underground Expedition
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Iceland's two underground wonders
Iceland's volcanic landscapes are dramatic above ground, but the secrets below are just as striking. Two trips stand out for travellers who want to go underground near Reykjavik: Þríhnúkagígur, usually written Thrihnukagigur, and the Raufarhólshellir lava tunnel. Both are safe, guided experiences, but they feel completely different. The choice comes down to how you want to spend your day, how much you want to walk, and what sort of underground world you want to see.
The two experiences you are most likely to weigh up are the Thrihnukagigur Volcano Guided Hiking Day Trip and the Raufarhólshellir Lava Tunnel: Underground Expedition. The second is the easier booking for a shorter trip, and it earns the top recommendation here. The first is a bigger adventure with a hike and a vertical descent into a volcano chamber.
Choosing between them starts with how much time and energy you have. The lava tunnel is a walk along a broad passage that lights up with mineral colours. The volcano is a hike followed by a descent into a huge open vault. Both get you inside Iceland's volcanic story, but they stay with you in different ways.
Why Thrihnukagigur is like nowhere else
Thrihnukagigur is a volcano whose magma chamber is empty. The last eruption took place about 4,500 years ago, and the lava drained away through a deep underground rift, leaving a hollow space.[7][11] The chamber is about 120 m deep, and the bottom floor measures 50×70 m.[7] This empty space is what makes the descent possible, and it is a rare thing to stand inside.
The volcano was discovered in 1974 by cave explorer Árni B. Stefánsson and opened for tourism in 2012.[12] It is not a place you can wander up to on your own: the only ways to reach the base are the guided tour hike or a helicopter.[8] For most visitors, that means joining the guided day trip and walking across the lava field with a group. The route itself gives you a sense of scale before you even drop below the surface, with the crater appearing only near the end.
With the chamber hollow, the light changes as you look up from the floor. The rock around you is not black only; it carries reds, greens, yellows and golds. You do not need to be a geologist to feel the scale of the place. The colours are not subtle, but they are easy to miss if you rush; take a moment to look up from the floor and let the size sink in.
The lava field path leads across a mossy ridge toward the cone of Þríhnúkagígur.
Walking and riding into the Thrihnukagigur crater
The Thrihnukagigur day trip starts at a meeting point in Bláfjöll about 30 minutes by car from Reykjavik on paved road.[10] From there you walk to the crater on a path that is about 3 km (2 miles) each way and usually takes about 45 minutes.[8] You will cross mossy lava and rocky ridges, then arrive at the cone with its opening at the top.
Inside, you have about 35-45 minutes from the lift down to the lift back up, with around 30 minutes free on the chamber floor.[9] The walls glow with colours left by mineral deposits from the last eruption.[13] The tour runs May 5th to October 30th every year and has a minimum age of 8 years old.[8][9] The full GetYourGuide trip lists a duration of 4 - 6 hours with pickup available.[3]
The descent itself is not a walk down stairs. You step into a lift with the rest of your group and drop through the narrow opening while the daylight shrinks above you. When the lift stops, you step out onto a floor that feels more like a vast hall than a cave. It is cool, still and strangely quiet, and the chamber walls rise high overhead in streaks of mineral colour.
What the Raufarhólshellir lava tunnel offers
Raufarhólshellir is a lava tunnel formed when a river of molten rock cooled and drained. The cave formed during the Leitahraun eruption about 5200 years ago, and the total tunnel length is 1360 m, with the main tunnel running 900 m.[1] Unlike Thrihnukagigur, you do not descend into a chamber. You walk along a passage that was once filled with lava.
The Raufarhólshellir Lava Tunnel: Underground Expedition is the listing we recommend. It lasts 1 hour, includes a live guide in English, and is priced from US$72.[2] Reviews give it 4.69 from 1,956 reviews.[2] You can reserve now and pay later, and cancel up to 24 hours in advance for a full refund.[2]
The tunnel is a place for slow looking. There are ice formations in winter, odd lava shapes on the walls, and a cool silence that feels far from the city. The path is even underfoot, so you can focus on the rock rather than your footing. The passage is wide enough that you never feel cramped, and the guide points out details in the rock that you would walk straight past alone.
from US$72
Raufarhólshellir Lava Tunnel: Underground Expedition gives you 1 hour inside a 1360 m lava tube with a live English-speaking guide.[1][2]
How the two trips feel on the day
Thrihnukagigur is an active day out. You walk for a while, descend in a lift, spend time in a huge open space, and then climb back out. The scale is enormous, and the colours on the walls are the reward. The Raufarhólshellir Underground Expedition is more compact, with no mountain hike and no vertical descent.
Both are guided in English.[2][3] The Thrihnukagigur tour also has guides speaking Icelandic.[3] For most travellers, the Raufarhólshellir trip is easier to slot into a day, while Thrihnukagigur asks for a bigger chunk of time and a longer booking.
Which one leaves the stronger memory is personal. Some travellers talk for years about standing inside the volcano, while others prefer the long glowing corridor of the lava tunnel. Both are legitimate ways to understand Iceland's volcanic past, and both let you do it with a professional guide. Think about the day you want: a focused hour underground feels very different from a full expedition, and both will leave you with stories.
Choosing between Thrihnukagigur and Raufarhólshellir
Pick the Raufarhólshellir Underground Expedition if you want a straightforward guided tour of a lava tube, a lower price, and an easy way to see volcanic plumbing from the inside. Pick Thrihnukagigur if you want the full ritual of hiking across lava fields, riding a lift into a hollow volcano, and standing in an enormous chamber. There is no wrong choice, but the two book very differently.
The day trip to Thrihnukagigur costs from US$432, while the Underground Expedition is from US$72.[2][3] The Raufarhólshellir Underground Expedition lasts 1 hour, which leaves room for other sights in Reykjavik or a soak afterward.[2] If you want to visit the same tunnel by bus from Reykjavik, that tour runs 3 hours and costs from US$153.[4]
If you are still torn, think about the rest of your itinerary. A shorter underground tour leaves time for the Golden Circle, a museum, or a long meal in Reykjavik. The volcano trip will claim most of the day and feel like the main event. That is not a reason to avoid it, so long as you know what you are signing up for.
Booking the right underground trip
Book the Raufarhólshellir Lava Tunnel: Underground Expedition directly through GetYourGuide, where you can check starting times, reserve now and pay later, and cancel up to 24 hours in advance for a full refund.[2] It is the smoothest way to get a guided hour inside a long lava tube, and the booking gives you flexibility if plans change.
If your heart is set on Thrihnukagigur, book the Reykjavik: Thrihnukagigur Volcano Guided Hiking Day Trip from US$432.[3] The tour runs May 5th to October 30th, has a minimum age of 8 years old, and has pickup available.[3][8][9]
On the day, arrive with comfortable footwear and a sense of curiosity. Your guide will handle the safety briefing, the route, and the stories. All you need to do is show up ready for somewhere extraordinary. Whether you choose the lava tunnel or the volcano chamber, the underground will not look the same afterward.
GetYourGuide ratings compared
Underground tour prices at a glance
From-prices in USD from GetYourGuide:[2][3][4][5]
When to book and go
Plan your underground trip
Pick your experience
If you want a short lava tunnel walk, choose Raufarhólshellir Underground Expedition. If you want a volcano hike and magma chamber, choose Thrihnukagigur.
Check the time
The Underground Expedition lasts 1 hour. The Thrihnukagigur day trip lasts 4 - 6 hours.[2][3]
Book with flexibility
Both listings offer reserve now and pay later and free cancellation up to 24 hours in advance.[2][3]
Dress for the underground
Wear sturdy shoes and bring a warm layer. Lava tunnels and volcano chambers can feel cool, and the Thrihnukagigur hike crosses open lava country.
Confirm pickup details
Pickup is available on the Thrihnukagigur day trip. For Raufarhólshellir, check availability for starting times.[2][3]
Book your trip inside Iceland's lava tunnel
from US$72
