The city
Prypiat, basically a stone's throw from the Chernobyl site, will be a ghost town for the next few centuries. It is unsafe except for "the briefest of visits," as every website on teh internets will tell you. But I'm look for specifics.
Help me with my detective work, fine citizens of L_D.
Realistically, how long could a person stay there safely? Days? Weeks? Months? I think it would be wonderfully creepy for a villain to drop a character in the middle of Prypiat, not telling him where he is (but knowing he'll figure it out from one particular landmark), then leave a note on the landmark saying something like "congratulations! you have exactly [time period] from your arrival to get out before you'll be infected and get cancer LOL HAVE FUN."
This may not, however, be sufficiently menacing, especially if someone could stay for months without serious danger. Of course it's just an adventure story, so I can stretch the truth a bit...I just want to know if I'm even close to reality. Just being in a ghost town at all is pretty damn creepy, so I can make the story work without the DEATH element.