Is already mapped within the perimeter of the building, implying inside. Node contains the key wheelchair:description=Access via Exhibition Road entrance an lift to Ground Floor. On north wall between Accessible toilet and "The Kitchen" in the Museum Red Zone. 

Museum's own map https://www.nhm.ac.uk/content/dam/nhmwww/visit/map/Museum-map.pdf describes it as a Water Bottle refill point.