​Risk of Rain 2 Obelisk is used to unlock Mercenary, one of the many new characters. It's not as difficult as it sounds, but people need to get a bit lucky. It's not known how to summon the Celestial Portal, but you need the portal to unlock the Mercenary. So far, people have just randomly come across the Celestial Portal while they adventure, so I advise doing the same thing.

Once inside, you need to find the Obelisk.

Risk of Rain 2 Obelisk: How to Unlock Mercenary

The process once you reach the Obelisk is fairly simple, but it's not an easy trip to get there. You have to do some dangerous jumping and climbing to reach the Obelisk. Once you do, interact with the Obelisk and watch as your character dies. But hey, you unlock Mercenary at least. 

Risk of Rain 2 became available for early access on Thursday, March 28 with new partner Gearbox Software, developers of the Borderlands series and the recently-announced Borderlands 3. It features similar gameplay to the original with expansion on the core gameplay of level-based procedural generation, character progression, item recovery and defeating monsters. A major addition was the shift from 2D to 3D.

Photo courtesy of Hopoo Games