Shoom

Me and a friend dug a 6x8 canal through a ~400 block mountain with bronze pickaxes, I think it took us something like 30 pickaxes and maybe 20 hours on and off (we wont be making another one anytime soon) If you value your sanity (and metal) I think an above ground stone path is better, the movement speed buff is quite significant, stone paths are also a good sink for excess stone and dirt when your crates are starting to fill up.

As proof, I've attached a picture of the aforementioned criminal. We painstakingly brought him back to town after the crime (we were new to the game at the time and thought we could tame him) ((moose milk is not a thing)) Initially we kept him in a pen outside the house along with the chickens but after innumerable acts of murder later we decided to move him inside the town barn, where he has spent the past 3 years and where he will remain until the moose taming update.

My buddy was standing on the edge of that pit, probably 50 blocks deep, just looking to see if we had missed any potential ore or ruin entrance (as you do when you pass that pit) suddenly a mad moose came charging out of the bushes behind him pushing him all the way to the very bottom, next 15 minutes were spent gathering sticks for ladders.