After reading through Jason's recent memories, there was little of note besides the extensive memories of him sleeping with his female teammate, Artemis.
The Hall of Everything was now dilapidated beyond recognition. The rupture of the Source Wall appeared to have affected the place as well, and the secret passage that connected different temporal and spatial nodes of Earth-0 could no longer bear the strain.
As for why Jason had come here, it was because he suspected that the person organizing the gathering here was "Joker's Daughter," Duela Dent—a pitiful young psychiatric patient.
She believed she had some sort of connection to Joker and called that lunatic her father, but she was actually just an ordinary underage patient. If she was related to anyone, she was only an extremely distant relative of Two-Face—so distant that, by Chinese standards, she was well beyond the fifth degree of kinship.
Even so, during the period when Joker had faked his death, the somewhat unhinged Batwoman had treated her as the real Joker and viciously beaten her in the sewers. The girl then lost her footing and fell into a sewage waterfall leading even deeper underground.
Because Batwoman had believed Joker was dead at the time, his heart had turned to ashes. He had no interest in doing much of anything, and he did not even pursue her to check on the girl's condition, merely turning and leaving.
Jason, who had already fallen out with Batman and only occasionally returned to Gotham, had happened to tail his adoptive father. Seeing this, he secretly went down after her. He rescued the girl and hid her in the juvenile reformatory where he had lived before being adopted. It had been abandoned for years, making it the perfect place to treat her injuries and hide her.
Her