Assemble in arena

"Assemble in arena" is an objective in the sidequests Hyperion Slaughter: Round 1 in Borderlands 2

Walkthrough

Head to the North from the entrance of the Ore Chasm. The door will open and let you into the main part of the arena itself. Head over to the big shutter doors in front of you in the ground and stand on them.

Next Objective

Complete Wave 1