You must possess all four Orbs of Command (from the Orc Prides), and use each one at its matching pedestal, to unlock the exit to the High Peak.
Upon placing an orb on a pedestal, a boss related to that orb will spawn. These bosses include the Crusher, the Neverdead, the Dragon, and the Silent Death. The bosses need not be defeated to enter High Peak. Merely placing the orbs onto the pedestals is enough to open the exit at the far end of the tunnel.
You keep the orbs after using them on the pedestals.