I think I've discovered why I love this game so much: When I was a little kid I always loved making tunnels in the sand at the beach, but it would always collapse, but with Minecraft is doesn't (at least that I've seen)
I'm trying to connect a mine that goes straight down through a mountain to the edge of the base of the mountain so I don't have to climb the side every time to get to my other mine and it's hard as balls
Iron should really be nerfed, there's too much in caves when you least need it, or atleast for me :(
I'm going to guess you're not making minecart tracks yet?