What happens at the London dungeons?

What happens? Not a lot. They relieve you of a good chunk of your money, in exchange for some cheap (and I don't mean inexpensive) thrills, themed around such delightful subjects as executions, torture, and general misery.

it's like a wax works combined with a walking ghost train with people dressed in scary Halloween type outfits telling stories and jumping out, I think there is a museum or display or "nasty" items as well

It's a museum with recreated dungeons, torture chambers and executions