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To unlock Luminescent Cavern in Fisch, find the three underwater pedestals in the Desolate Deep and interact with them to reveal the three keystones your character needs. The required set is randomized from nine possible keystones, so check the pedestals before visiting any locations. Collect only your three matching stones, place them on the pedestals, then swim through the opened crack and river.
Find the keystone pedestals first
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Equip diving gear and descend from the Red Buoy behind Sunstone Island into the Desolate Deep tunnel.
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Look for the Mysterious Crack and the three pedestals along the underwater tunnel. Tunnel directions can be described differently between guides, so use the crack and pedestals as your landmarks.
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Interact with the pedestals to reveal the three keystones required for your character. The combination is randomized; do not travel to all nine locations unless you want to collect optional extras.
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All nine possible keystone locations
Coordinates below are approximate X, Y, Z positions transcribed from Beebom’s guide and the Fisch fan wiki. The sources differ by a few units for some stones, and the coordinates are not official game coordinates. Use the landmarks to confirm each spot in-game.
| Keystone | Island or area | Approximate coordinates (X, Y, Z) | Landmark or access note |
|---|---|---|---|
| Cliff | Castaway Cliffs | (473, 230, -2159) | Look for a gap beside a ledge toward the island’s second level. One guide describes a longer route by ladders, faction leaders, a camper, and trees; use the ledge landmark if the coordinate does not lead directly to it. |
| Mushroom | Mushgrove Swamp | (2666, 130, -717) | Check the boat near the Alligator abundance area, also described as the rowboat at Alligator Marsh. |
| Fossil | Ancient Isles | (about 6065–6068, 225–226, 260–261) | Look near the Merchant for a pile of wood lifted by cranes; another guide describes a wooden crane moving a fossil. |
| Snowflake | Snowcap Island / Snowburrow | (about 2787–2788, 153, 2602–2603) | Enter Snowburrow through Snowcap Cave by interacting with cracks to open the hidden passage. The precise interaction details are not confirmed by an official source. |
| Volcano | Roslit Volcano | (about -1970, 175, 268) | Look inside the volcano; descriptions place it on a middle stone or a thin platform near lava. |
| Skull | Forsaken Shores | (about -2797, 209, 1542–1544) | Find it near the pirate NPC associated with fixing the map; another guide points to the open eye socket of the central skull. |
| Lightning | Grand Reef | (about -3406 to -3409, 134, 262) | Search the small islands in the reef archipelago. Descriptions place it left of the Shipwright island or on the smallest island between rocks. |
| Turtle | Terrapin Island | (about 57, 149, 2032–2033) | Look in Terrapin Hideaway, near a barrel. |
| Sun | Sunstone Island | (about -935 to -937, 223–227, -984 to -983) | Inside Merlin’s Hut, near the door or a barrel. |
Place the matching stones to open the cavern
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Travel to the three locations matching the pedestals’ requirements and collect those keystones. If Snowflake is required, first open the hidden Snowburrow passage inside Snowcap Cave.
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Return to the Mysterious Crack and place each matching keystone on its pedestal. Beebom’s guide says placing a nonmatching stone triggers an error indicating the correct one.
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After all three required stones are placed, swim through the opened crack and follow the passage and river into Luminescent Cavern.
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What to know about the location information
The Fisch fan wiki reports that Luminescent Cavern was added on September 20, 2025, in update 1.50.0, and its page was updated September 25, 2026. The addition date is a fan-wiki report, not independently confirmed here against a developer update log. Beebom published its guide on September 21, 2025, and Droid Gamers published its walkthrough on October 6, 2025. These are secondary guides or fan-maintained sources, not official Fisch documentation; map locations and puzzle mechanics may change in later updates.
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