Abandoned Factory.

It's not really a factory but I couldn't think of a better name for it.

Abandoned factories are uncommon structures that generate underground in the over-world but they never generate below Y=0. They are relatively easy to find as the entrance will be connected to a cave.

The purpose of the structure is to teach players how the crafter and copper golem work. Inside, there will be a redstone contraption at one end showcasing how the crafter works. There will also be one or two copper golem statues next to a copper chest with some items already in it.

The reason for this post is that the crafter and copper golem are quite complex features which have little information around how they work so they may be confusing to new players. This structure would allow players to learn more about these two features.