Olann Island is a Minecraftworld you can download and add to your saved games. It's one of the most impressive creations we've seen in Minecraft.
Apparently made in 10 days, Olann Island is an attraction resort with a things like a golf course and huge casino. Best of all there is a massive working roller-coaster and water flume. You can place a mine cart on the roller-coaster and ride it, and climb the stairs to the top of the flume and float down to a waterfall.
To play, simply unzip the folder and move it into your Minecraft Saves folder. It will then be available to play next time you open Minecraft.