May Kohanim visit Hayden Planetarium in New York City? The planetarium in question is adjacent to the Natural History Museum. Issues in question are presumably sof tumah latzeit (the idea that the impurity will eventually leave, therefore rendering the exits impure) in conjunction with ohel (the idea that the roof might transmit the impurity from dead mummies and skeletons to the planetarium).
I am not familiar with the planetarium in question, but I believe that it has its own entrance, which might mitigate the issues involved.