the last 300 or 400 feet of bertha, it's this really narrow strip that we call the plank. [ sighs ] so hot. >> holy shit. i just went from "everything's fine" to, like, "we need to move." the plank is like 10 feet wide. on your left side, you got a bunch of rocks. on your right side, you have 5,000 feet of air. if you fall anywhere on that, there's no rescue. it's just a recovery mission. [ sighs ] >> this is real deal to come down this. >> yeah. >> all of bertha is a no-fall zone. every step you take has to be a very sure step.