At the start of the chapter, talk to Lilysse in your bedroom. Once done, head to the lobby and talk to Lilysse when you have the chance. Check out and accept the new quests from Simon then prepare to leave. Head to the Roschester Subway Line > Market Station then continue north once again. Head to the same are where you fought the gargoyle and recovered Lilysse's ring earlier. In the room to the east, there's a red chest. Loot it then head to the NW where the newly opened doorway is located.
The amusement park is home to a lot of new potential servans like Plumie, Wolf, Toy Soldier, and Bomb. There are also a lot of traps scattered in the area and ambushes so be careful when progressing. From the train station entrance, head north and destroy the pile of crates to the north to find a chest behind it.
Continue west then south to encounter bombs. Deplete their HP then quickly move away before they detonate to avoid getting caught in the explosion. Destroy the pile of crates to the south then cross the spike trap on the ground to reach the chest in the other side. After looting the chest, continue further west and take out the enemies that will intercept you. Move on to the next area.
In the next area, you'll find several giant bombs that will only detonate when go get near them or when touched by your servans. There should be enough time for you to dodge so carefully trigger them one by one as you head west. Before reaching the split path, loot the chest behind the fountain to the south.
From the split path, the one going left is filled with more giant bombs and spike traps. There's a chest containing a fetish in the middle. The path going north leads to a couple of crate piles that will allow you to access the open stage to the NE with several plumies.
Both paths will reconvene near the exit to the next area and the door portal. Use the door for now to go back to the hotel and make the necessary preparations for your next excursion.