The Hoover Dam checkpoint building is a makeshift shack built on top of the Hoover Dam. It is inaccessible to the Courier until the final quest. The checkpoint building is constructed with scrap materials, with lockers and metal boxes strewed about the room. There is nothing of value to take, unless the Followers of the Apocalypse have been convinced to help NCR, in which case there will be a medical supply kit inside. In the room, there is a ladder that leads to a watchtower that looks over Hoover Dam.
Against the southern wall, a terminal can be found, which grants information about the dam's generators. There's also an option to run a diagnosis of the generators. If the Courier has a detonator in their inventory, it's possible to rig the generators to detonate them. Detonating them will show an EMP-like effect around the checkpoint, killing any Legion troops on the other side of the checkpoint during the NCR quest Eureka!.
The Hoover Dam checkpoint appears only in Fallout: New Vegas.