Are you trying to solo it? You need someone outside of the portal at all times or you get "lost in time" and wipe. But once you pick up the relic, you and the other people who were teleported in there with you need to kill 6 oracles while someone on the outside is opening up the portal. Hold your grenade button to cleanse the other players in there with you before they go completely blind. Once you kill all 6 oracles, you need to hurry outside and preferably go to the middle in front of Atheon (in between the 2 portals) and hold down cleanse to protect the rest of the team from harpy's/Atheon while they DPS. Edit: Forgot to mention that a few enemies spawn in there too. On Mars/Future/Left, there are 3 Hobgoblins. They will not notice you until you jump or attack them, so don't jump up super high in the air to slam them as this may get you killed. Go around this small rock on the right and jump up to slam them after you get kind of close to them. On Venus/Past/Right, there is a Minotaur and a few Goblins in there. You can jump up as high as you want here to just slam everything at once. The Minotaur will take a few hits before dying, but teammates should through grenades/tether at the enemies here to help if they can, not on mars though, that can get you killed.