Likely, the entrance can only be opened with Light & Dark. Like the incident which gave birth to the Awoken and which also opened the way to the Dreaming City. Same thing for charging the Blind Well to gain entrance to the Shattered Throne. Maybe by using an immense amount of Light in Eleusinia and Darkness in the Dreaming City? By the looks of the 3rd Curse week, Darkness is covered, but not the immense amount of Light in Eleusinia. Maybe that's why TtP says 999 Light, which is a maxed out Light level. A solo guardian with a maxed out power level being stripped of their Light like what happened in the Savathun's Song strike. Both Quria and Savathun are deceiving us. The only real being we can trust is actually Riven. Riven says she wasn't even part of Savathun's plan, so having Riven being described as bait so the Guardian can be tricked into searching for the Distribuatry is also a trick. If Riven wasn't part of plan, the overall end result of the Dreaming City being as it is wasn't really affected by Riven's death. (I mean it was, but Savathun didn't need Riven to get the same end result) It's merely a distraction from the real truth.