Penumbra: Overture - Episode 1

Key puzzle

The puzzle where a key needs to be retrieved by putting a newspaper under the door was also used in Fiend, Thomas Grip's first real game.

References

The crowbar you can find on Lake Utuqaq has the name "Freeman" on it, probably due to Gordon Freeman the protagonist of Half Life series. The glove worn by the hand holding the crowbar also looks like those Freeman usually wears in those games.

Whispers

When approaching an artifact, some distorted and incomprehensible whispers can be heard. These are actually sentences in Swedish played backwards. Not all of them are clear enough, but one of them says: Det är ett väldigt snyggt spel har du någonsin spelat ett sånt spel (It is a very nice looking game - have you ever played such a game?)