Stop player from climbing mountains I want to create an open world FPS game with the BGE. Is there an option with character motion that allows the player to only walk on ground that is (for example) less steep than 10°?

I don't want to place invisible walls next to every mountain in my game.
Under your characters physics settings select "actor" as physics type. Then there should appear an option step height. Increase or decrease this value as you like.