dark tourism is the visitation to sites that are established that have an association with death and disaster, some sites however, are accidentally linked to dark tourism, these being 'fun factories' which hold an entertainment factor, such as the London dungeons etc. sites that are purely dark tourism based are sites which are established to show death or disasters, like the concentration camps. although there is the argument of when dark tourism crosses into heritage, there is no evidence to suggest a timeline of how far back in history dark tourism becomes heritage, as many people visit such sites as they have heritage ties or interests.
has that cleared it up a bit for you?