Penumbra: Overture - Episode 1 Trivia (Windows)
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 on the games.
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?)