Old Lumiere is a big area with two separate street sections, a manor to explore, and a boss fight near the end. The team also splits up partway through, so be ready for that. Here is everything you need to get through it.
Old Lumiere Entrance
When you enter, a voice greets you with “Welcome my friends, to Old Lumiere.” Keep walking forward until you see a magic rope. Use it to climb down to the lower level. At the bottom, look left to find Expedition Flag: Old Lumiere Entrance. Rest here.
Directly across from the flag is a Gestral wanderer named Mandelgo. He sells two Pictos: Longer Powerful and Healing Counter (20,400 Chroma each). His stock also includes Chroma Catalyst x10, Polished Chroma Catalyst x5, Colour of Lumina x3, one Recoat, and one Revive Tint Shard. You can also challenge him to a duel to unlock the Algueron weapon.
From the flag, follow the main path toward the large glowing swords visible ahead. You will reach an area of collapsed buildings where a cutscene plays. Monoco clears a path but accidentally splits the group. From here, you are playing as Sciel, Lune, and Monoco while Maelle and Verso are separated. Keep going along the main path until you see Expedition Flag: Right Street on your right. Rest and sort out your skills and upgrades for your current three-person party before moving on.
Right Street
Follow the path forward into an open area where two enemies are waiting: a Ceramic Chevaliere and a Steel Chevaliere. Beating them gives you the Battlum weapon for Maelle, which you will be able to use once the team reunites.
After the fight, look for a broken doorway on the left side and head down that path. Two more Ceramic Chevalieres are here. Take them out. Keep going past them, and you will find an NPC named Nusaro standing near a barrel.
Come back to the main area and go right. When you reach the edge, look for a white glowing light and drop down to collect 2,495 Chroma.
Return to the main area again and go left this time. Use the grapple to reach a rock, then grapple again to land on solid ground. There is a crawl space on the right: go through it to collect more Chroma. Come back out and deal with the patrolling enemies in the main area.
After jumping the first gap, walk to the ledge on the right and look down. There is a lower ledge below; drop down to it to find the Time Tint Pictos. Keep going down this path into a larger open field. Climb the ledges on your right to fight a Ceramic Chevaliere and two Steel Chevalieres. After the fight, follow the same path to the end to find a Colour of Lumina.
Head back to the main area, go left, and grapple to the other side. A Fading Man is standing here. Talk to him and he will tell you about the Paintress. Take the path to his right and keep going until a cutscene plays.
The cutscene happens in two parts. In the first, Sciel finds one of Esquie’s rocks. Sciel and Lune talk about Verso’s intentions, and Lune finds something unsettling after reading Journal Expedition 58. They decide to go find Maelle, worried she is in danger. In the second part, you see Maelle, Verso, and Noco together.
After the cutscene, you switch to playing as Maelle’s group. Check behind the broken wall on the right side to find a Colour of Lumina. Follow the main path to the Left Street expedition flag and rest.
Left Street
Head down the main path into an open field. Beat the Ceramic Chevalieres walking around the area, then go through the doorway into another open field. The path splits three ways here.
Take the left path first to collect 2,495 Chroma. Then take the right path, drop down onto a pipe, and grab the Polished Chroma Catalyst sitting there. Go through the hole in the pipe and use the Old Key to unlock the gate beyond it. The Journal Fracture Survivor is inside. Before leaving, pull the rope at the edge of the pipe to unlock a way back up.
Return to the main area and take the middle path. Beat the Ceramic Chevalieres patrolling here, follow the route, and turn right where you will find more enemies to deal with. After clearing them, a cutscene plays where Verso disappears and Maelle decides to continue with just Noco.
When the scene ends, you will see a grapple point on the ledge ahead. Use it to get up and look right for a Colour of Lumina. Drop back down to the main path and keep walking into an open field. Take out the lone Ceramic Chevaliere here, then follow the path to a broken bridge. Use the grapple to get across.
On the other side, you will see an archway on the left and a single Ceramic Chevaliere on the right. Go left first. A group of three enemies is patrolling near a Pictos. Defeat them and grab the Auto Rush Pictos. Come back, deal with the Ceramic Chevaliere on the right, and keep moving forward.
The path splits again near a building with a melted golden front. Go left and follow it to pick up a Polished Chroma Catalyst. Take out the Ceramic Chevaliere and Steel Chevaliere in the area, then use the grapple to cross. A large building is visible ahead in the background. Keep going until you reach Expedition Flag: Manor Gardens. Rest here before continuing.
Manor Gardens
From the flag, look toward the left boundary wall of the manor. Part of it is broken, go through the gap and turn right to find 2,495 Chroma near a gate next to a dead enemy. Come back and look at the left side of the garden. There is a door here. Walk up and interact with it to enter the manor.
The Manor
Inside, check the sink on the right to pick up an item called Renoir. On the left side, there is another door leading to a bedroom. The Journal Renoir is sitting next to the bed, grab it. Leave through the main bedroom door, and you will be in a hallway.
The door directly ahead is locked. Turn left and then left again and follow the stairs down to the main lobby. On the right side you will find Expedition Flag: Entry Hall. Rest if you need to, then go through the main door to head back out to Old Lumiere.
Manor Gardens (Return)
Back outside, walk toward the main entrance of the manor from the Manor Gardens expedition flag. A cutscene plays here revealing that Verso is the son of Renoir, the white-haired man. The boss fight against Renoir starts immediately after.
Defeating Renoir rewards you with three Polished Chroma Catalysts and the Melarum weapon. A final cutscene plays after the fight, and everyone returns to camp where they confront Verso about what he has been hiding.