Good answers!. I expect AlanK got it first.
The place is Trinity Site, where the first nuclear weapon was fired. The photo shows Oppenheimer & Groves (two of the most important people in the country) wearing regular clothing at ground zero shortly after the war. On open-house days you can walk right in & stand in that very same place. An hour's exposure here is about equal to 10 hours of normal background exposure.
Obligatory wiki here
I have another place in mind, but if anyone wants to post a puzzle - go ahead.