Main Gate Park stands at the original entrance to the secret Manhattan Project site, and its small building is a reconstruction of the guard gatehouse through which every resident had to pass. During the Project years, the gate separated the classified community from the outside world: incoming visitors were scrutinised, outgoing mail was read, and the entire site was fenced and guarded.
The park has interpretive panels explaining the security apparatus of wartime Los Alamos and photographs of the original gate. It is a small stop — fifteen minutes is enough — but it adds a physical dimension to the history that the museums can't quite replicate.