Night falls. The zombies are after me. Quickly thinking, I make a trapdoor instead of a regular door, so they can't get in. After a safe night, I use 10 torches, breaking and placing again, to make my mineshaft. I get 3 iron, and I place down a furnace and crafting table, in the middle of the caves, and make an iron pick. Then I find more iron, and eventually some diamonds, crafting while in the caves.