This one is located directly after Boss #5 - Tyr. Hidden behind the exit portal, there's an hourglass on the ground. This one is located directly after Boss #2 - Manifested Timeways.

You can drop the artifact using an extra-action button but another player must pick it up within 10 seconds or it will despawn. The Time-Lost Artifacts look like Hourglasses and while you have it, you cannot mount, or double-jump due to a debuff. Players have to pick up 4 time-lost artifacts through the dungeon and bring them to the end boss without dying to get Put That Thing Back Where It Came From. When you complete this, you get also get Ensemble: Infinite Acolyte's Regalia transmog which is account wide! You can see this on Driney_'s stream below:

If you complete Put That Thing Back Where It Came From, the last boss loot is upgraded to 441 item level which can then be upgraded further to 447 on the Myth track! Here's how to complete the Hard Mode Immortal Dawn of the Infinites achievement which causes the final boss to drop higher item level loot!

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