Tunnel stealth challenge
After the underground bridge, you arrive at some enemies in the tunnel. On Legendary there are a few Elites pacing around, and a few dozy Grunts. See if you can take them all out with stealthy whacks to the head. It's possible, but you'll need to time your movements carefully to get those nasty Elites. Patience is the order of the day. Once you manage that, continue the stealth work and see how many of the patrolling Jackals you can whack.