The original tagline that was used when advertising the film was 'They should have gone to Vegas'. But due to the massacre in Vegas that took place on 1 October 2017, the tagline has now been changed to 'They should have gone to Ibiza'.
The film was shot in the Carpathian Mountains of Romania.
The sign the hikers see on the trees near the cabin is the last rune of the Futhark (ancient Germanic alphabet) called Odal or Othala. It is pronounced 'o' and means 'property'.
Beside the Othala/Odal rune, the Algiz (also called Elhaz) rune can be seen on the trees and as the shape of a sacrificial pole. Algiz is the name conventionally given to the "z-rune" of the Elder Futhark runic alphabet, from the Common Germanic word for "elk" and it is thought to represent the divine might of the universe.
The creature in the film is actually based on a jötunn (race of Jötnar) from Norse mythology. This is mentioned with captions turned on, and was what the woman in the cabin identified the creature as to Luke.