It's mostly memorization. It takes practice, though, and I know it's not easy when you can't use sight as a reference. You can go by feeling- the way the ground is where you start out, the steps you take when you're moving, or the air flow, since just about anywhere you go has a sight breeze. [She licks her finger, lifting it up.] There's even one in here, if you can feel it- there's air vents, and a source somewhere down the tunnels.