I do believe the only instance you can find this dungeon is through the "For the King" campaign. As a part of the objectives in Act II, you will be tasked with collecting a Key Fragment from the boss at the end in order to enter the King's Maze. As such, if you enter the dungeon with some decent healing options and healed up, any enemies in rotation you could encounter shouldn't be dealt with too poorly; this is, of course, expecting you to be levelling and re-gearing your characters often.