Risk of Rain 2

This achievement requires you to end your run at the Obelisk. To reach the Obelisk, you need to enter the Celestial Portal, which is available at the end of Stage 8 (and every eighth stage after that). In case you're wondering how to reach Stage 8, since the game ends at Stage 6, you need to loop back to the first stage from Stage 5, Sky Meadow. In this stage, you'll likely notice the teleporter looks different than other stages. There are stone slabs around the perimeter of the circle. Before activating the teleporter, interact with the stone slabs first. They will reorient, lining up on either side of the center. You will also get some text on the left side in the text feed saying that the teleporter is now aligned with the planet. This means, upon completing this stage, you'll loop back to the first stage rather than going to the moon to beat the game. Finish the level, and you'll head to Stage 6, which will be one of the first stage options. Proceed as normal, completing Stages 6 and 7. On Stage 8, there will be a blue orb floating around the teleporter. Finish the teleporter event like normal, and the blue Celestial Portal will open next to it. Hop in to go to a Hidden Realm.

In this Hidden Realm, it might look pretty precarious to get down from platform to platform. Don't worry - platforms appear in set spots so you don't take tons of fall damage. And remember - fall damage isn't lethal. There also aren't any enemies here. Make your way to the bottom, and there will be a giant obelisk on the final platform. Walk up to it and interact with it twice (the second time is a confirmation) to obliterate yourself, ending your run. This will unlock this achievement, as well as a new playable character.

As a side note, if you end up here and decide you don't want to end your run, walk up to the obelisk, but then a portal will spawn down and off to the right. Head inside to return to stages like normal.