Japan had turned part of the London Underground into a theme park and I somehow ended up there with my brother. There were loads of rollercoaster-esque rides using the tube carriages, and some of the escalators had tuned into rides too.

On one of them, you had to imitate an animal given to you on a ticket at the top of the escalator before you got to the bottom (I got a chicken). At the very end, you could go outside and there was a giant ant that looked like it was from A Bug's Life with a really long neck. The neck had loads of ribs cascading down either side of it, and you had to sneak past without it noticing you.