I'm possitive that almost everyone has seen a mineshaft at one time or another. Who built them? Why? Well all I can tell you is that whoever built them was a profesional NOOB!!!! I have seen the fence posts on diamond, iron, lapis, gold, redstone, emerald, obsidion, mossy cobble stone, and over deadly lava pits that end up setting the whole place on fire. Once I thought about who built these and why. Then I wondered where did they go? Then I found out. It was when I was following some minetrack and I decided to ride it with my only minecart. It led into lava and I died. Plus you know those chests you find in them. Where did that stuff come from? Where did they get the mellon seeds that can't be found anywhere else? No one will ever know.