Where it sitsChapter 4 lava-pathway dungeon entered from the Temple of the Red Sun after Temple Guardian
Per Miraheze's Locations table, the Red Sun River is the third Chapter 4 (Excavation Exploration) location, sitting between the Temple of the Red Sun (where the Temple Guardian three-body split resolves and the Ancient Key drops) and Mount Red Sun (where Captain Trotter's lava fall unlocks Firebrand and The Ancients sits as the chapter final boss). The transition is a natural walk from the Temple of the Red Sun exit into the lava-pathway dungeon - no menu toggle, no quest flag. The Red Sun River is the chapter's puzzle-gating dungeon: the Grand Orb Puzzle is the only Notable Structure and the only verified Chapter 4 puzzle that requires three separate items (Sword, Hyperball, Orb) to solve. The temple's leftover spike-armor trash and the Captain Trotter post-Temple-Guardian dialogue funnel directly into the river. Plan the build so the Firebrand blade is in the inventory before crossing the Red Sun Bridge into the temple - the river's Flaming Horse and Flame Warrior trash layer Cone of Fire damage on top of the lava falloff, and the Grand Orb Puzzle does not pause for a re-equip.
LayoutLava walkway entry + Grand Orb Puzzle room + Medjed/Calypso/Trotter NPC cluster + Firebrand pedestal
The Red Sun River has four sub-areas in a fixed order: the Lava Walkway Entry (the entry room from the Temple of the Red Sun exit with the first Flaming Horse sentries and the lava falloff that does damage on every turn), the Grand Orb Puzzle room (the location's only Notable Structure, with the three-wheel mechanism, the colored-light diamond on the floor, and the pushable pillar that the Orb slot activates), the Medjed + Calypso + Captain Trotter NPC cluster (the Chapter 4 mid-route dialogue trigger where Medjed reappears as the Egyptian vendor, Calypso stays locked into the party for the upcoming Mount Red Sun boss chain, and Captain Trotter appears in his post-Temple-Guardian dialogue state), and the Firebrand pedestal (the post-puzzle pickup station that drops the Firebrand blade on Grand Orb solve). The Grand Orb Puzzle is the chapter's only three-item puzzle and the only Chapter 4 mechanic that requires both color alignment AND wheel alignment to clear.
Grand Orb PuzzleSword aligns the wheels, Hyperball changes the light color, Orb fills the pushable pillar
The Grand Orb Puzzle is the most-cited Chapter 4 mechanic that no YouTube guide frames cleanly. Per Miraheze's Notable Structures field, the Grand Orb Puzzle is the only Notable Structure in this location and the hardest Orb Puzzle in Demo 4. The puzzle works as: SWORD rotates the two wheels until the scorch symbol is formed, HYPERBALL double-jumps on the diamond-shaped floor to change the light color until the light turns red, and ORBS places the red orb on the purple pushable pillar after the pillar is moved. The prophecy on the ground reads 'UNDER THE GAZE OF THE scorch IN THE SKY CONSPIRE, HEAT OF red FALL TO US, SAFETY WHICH WE DESIRE. QUELL THIS HEAT firebrand DOES PROVIDE.' - this is the verify check that tells the player which wheel symbol to align (scorch), which light color to set (red), and which item to fill (Firebrand / red orb). Most 'red sun river puzzle' / 'grand orb puzzle' / 'block tales demo 4 last puzzle' Reddit threads cluster around players who had all three items but did not know the order. Plan the Chapter 4 inventory so the Sword, Hyperball, and a red Orb are all in hotbar slots before entering the river - the puzzle is hard-coded to the three items in sequence, and the puzzle does not pause for a re-equip.
