It is occupied by Neil, a friendly super mutant. When the Courier approaches the area, Neil will run towards them and initiate conversation. He will share valuable information about the area up the road, Black Mountain, and give you the quest Crazy, Crazy, Crazy.
Neil's shack consists of a makeshift shelter that provides little protection from the elements. He has a table outside the shack with his radio (which is constantly turned on), as well as a mattress on the floor that the Courier can use for sleeping.
Neil's shack is the closest landmark to the geographic center of the Fallout: New Vegas base game world map.
Neil's shack appears only in Fallout: New Vegas.