SCP-087.
SCP-087, also known as the Stairwell, is a stairwell located on-campus at a location that has since been classified by the SCP Foundation, and also the lair of what has been designated SCP-087-1. The doorway leading to SCP-087 is constructed of reinforced steel with an electro-release lock mechanism. It has been disguised to resemble a janitorial closet consistent with the design of the building. The amount of volts required to open the door are unknown, having been classified as well.
SCP-087 is an unlit platform staircase, which descends 13 steps before reaching a semicircular platform of roughly 3 meters in diameter. The design of SCP-087 limits subjects - usually D-class personnel - to a visual range of approximately 1.5 flights. A light source is required for any exploring SCP-087, as there are no lighting fixtures or windows present. SCP-087 seems to absorb excess light should the source be brighter than 75 watts.
Subjects report and audio recordings confirm the sound of a crying, pleading child located at least 200 meters below the initial platform. However, as a subject descends the staircase, so to does the "child" (except for in the third experiment, where just before the camera went out it was revealed the child was closer than before). It is currently unknown if SCP-087 has an endpoint.