In Eyrbyggja saga, the berserker Halli wants the farmer Styr's daughter, Ásdís. Styr says: first, some work. A road across the lava, a boundary wall and a sheepfold. Meanwhile Styr has a bath-house built, dug down into the ground, with a window over the oven so that water can be poured on from outside. And that house, says the saga, was extremely hot.

The berserkers finish the road and come home exhausted. Styr thanks them and offers them a bath. Once they are inside he shuts the trapdoor, piles stones on it and lays a soaking-wet ox-hide by the way out. Then water is poured on the oven through the window, until the berserkers cannot bear the heat and run at the door. Halli breaks out and slips on the hide. Neither of them survives. They are buried beside the road they built, in a lava hollow so deep, the saga says, that you see nothing from it but the sky. The daughter is promised to someone else.

The saga was written down in the Middle Ages about events around the year 1000: literature, not a police report.

In Finland, if your future father-in-law offers you a sauna, say yes. But let him go in first.

Would you go in first?

Sources: Eyrbyggja saga, chapter 28 (the Old Icelandic text; our working translation).
The carved stone in the film is our drawing in the manner of Viking-Age rock carvings and picture stones; no such stone exists.
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