The Basement Key is a key Travis Grady obtains in Silent Hill: Origins. It is located in the second floor TB Ward of Cedar Grove Sanitarium. According to a previously found memo, a patient swallowed the key and was taken to the TB Ward to extract it. To acquire it, the player must first complete the Iron Lung Puzzle.
It can then be used to access the basement floor of the sanitarium using the south-east stairwell.