Minecraft wiki entry for Things_to_do_when_bored, associated text: Rails and minecarts can be combined with blocks to create roller coasters. These can have drops, sharp turns, and scenery. Although they are usually built in the Overworld, they can also be built in the Nether, or a portal could even be used to make a roller coaster that travels through both dimensions interchangeably. There are infinite possibilities. See Tutorials/Building a rollercoaster for more info.