Things are pieces used to build a portal to the next world. Each Thing has a designated set piece that will spawn with it. There are five different pieces, and as such, 5 different Structures.
Things will tend to spawn with large distances separating them, and as such will encourage the player to explore the world to find all of them. A Divining Rod will help locate the Things. One is given to the player in Adventure Mode, or can be crafted.