I've gone on the Ghost Bus a couple of times, and really enjoyed it. I agree that it's a little expensive, but it's good fun, and not scary at all - unless ghost stories bother you. The bus takes you around to various supposedly haunted sites in Dublin, where the guide will tell you all the gorey/creepy details of what happened there. It's fascinating - and educational - if you're interested in history at all. There is a lot of getting on and off the bus involved, though, so it's worth dressing appropriately. Not much fun standing around in a freezing cold graveyard in the depths of Winter with no coat on!