I've been a bit bored this lunchtime so I was reading about failed theme parks on the interwebs.
Every time I drive towards the M1 I see brown signs for the 'American Adventure' still in place, sadly it closed before I moved to the area. Apparently you could wind the staff up by forcing them to say 'Howdy' a lot, and there was a ride themed on the hit TV show 'Gladiators'.
Does anyone remember a Noel Edmonds theme park once existing? I don't know anyone that actually visited it, so it might be one of those 'urban legend' things.
Also a lot of abandoned theme parks in Japan - http://www.michaeljohngrist.com/ruins-gallery/theme-parks/