Surt is, of course, the ruler of Muspelheim, the fire giant who is said to destroy all of creation in accounts of Ragnarok, notably the Voluspa.
Surthshellir is a lava tube cave, an eminently desirable residence from a fire giant’s point of view. The cave used to be nearly inaccessible until relatively recent times, when a partial ceiling collapse opened up a sort of “skylight”. As a bonus, the cave boasts an underground stone wall and caches of smashed bones (one of the side caves is called “Beinaheller”–Bone Cave.)
The Icelandic settlers apparently recognized this early on, when Thorvald Thordarson traveled there to offer a drapa to Surt.
I found it interesting that the archaeologists researching the site can’t quite agree about what went on there. Some favor the hypothesis that it’s the abandoned lair of a famous outlaw band. (There are stories in Iceland to this effect–actually a good many over the centuries.) This contrasts with what some other archaeologists think, which is closer to their usual position when they don’t understand something: wave your hands vaguely and mutter ‘It must have had religious significance.’
Well, in the case of Surtshellir, I’m going to side with the wavers and mutterers. Let’s start with Thordarson’s drapa. I think that incident fits right in with other accounts of Iceland’s new settlers immediately recognizing some sites on the island as sacred (for example, Helgafell). In Surtshellir’s case, ‘unhallowed’ might be a more appropriate designation. So why a drapa, which is usually a poem of praise? Why would Thordarson celebrate a world-destroying fire giant? I would guess that it’s the same tendency that led those who feared fairies to refer to them as ‘The Good Folk’. Thordarson may have reasoned that if he praised Surt, the giant might stay put and rest on his fiery laurels.
The smashed bones piled up in the cave certainly seem like the remains of sacrifices. The bones weren’t cooked, but what need is there to pre-roast offerings to a fire giant? He can obviously handle his own cooking.
Then there’s the little detail of the fortress wall built across the cave, eight hundred feet away from the entrance. When it was built, there would have been no natural light down there. And no signs of human occupation have been found past that point. So I don’t put much stock in the idea that the wall was some outlaw’s defense structure. It was built to keep something in, something that might otherwise erupt (literally) from the dark places under the earth.
There’s also the incident of Snorri Sturluson’s son being mutilated, then left on the wall to die (amazing that he didn’t–even post-Viking Age Icelanders must have been pretty tough). It’s really hard not to see this as his enemies killing two birds with one stone, combining revenge with a sacrifice to Surt.
As for the stories about the cave being an outlaws’ hideout, I’m guessing that tradition arose to provide a convenient explanation for avoiding the cave, after Christianity had driven heathen culture and religion underground (no pun intended). The only thing I wonder about is, why not a tradition that the Devil lived there, at the entrance to the Christian Hell? Maybe just because outlaws were better characters for sagas.
Anyway, the cave is still there, Iceland is still there, so the strategy to contain Surt must have worked!