I’d advise you to pre-book as they let a group of twenty in every ten minutes and having a ticket puts you in the next group. It isn’t cheap (£10.99 for adults on the door) but vouchers can be found with a bit of looking.
It is a cross between a museum and a haunted house walkthrough with a number of set pieces led by actors in costume & makeup “celebrating” the bloodier parts of York’s history such as the black death, the Romans, Vikings, Judgings & Torture. The Gunpowder plot is also re-enacted along with the hanging of Dick Turpin. Some of the actors were suitably deprecating along the way and a highlight had to be the future ghost exhibit consisting of an empty room with only a brush in it, referred to as the broom of doom.
A trip to York isn’t complete without a visit to Lakeland, the kitchenware store with lots of great gadgets. I particularly liked this jug that you can fill without having to squint at it from the side like our other ones. They also sell Aussie Licquirice, so we stocked up with green, yellow and dark brown.