The long path to the left of Rodin's portal starts a scene, and then the road falls apart into the lava behind you as you run. You can't walk back to the main road this run. Before you go, have the Mystic's Painting from the portal, the Verse 6 angel portal, the Figure Box on the tower, the crow, the Verse 5 Niflheim and the summon-only chest, plus everything from the courtyard and the lava pit. A missed one can be collected later by replaying the chapter from Chapter Select once the chapter is finished.