The Sacred Relics in Shells are three quest items that gate access to the Sacred Mountain island. They only appear after you accept a specific quest, and they always spawn on the same three islands, even though the exact spot inside each island is randomized per player.
Quick answer: Talk to Virek on the small island next to Sacred Mountain to start the quest, then collect one Sacred Relic each from Sea Stack Islands, Crescent Shore, and Bay Island, and return all three to Virek.

Start the quest with Virek
Sacred Relics do not spawn in the world until the quest is active. Trying to search the islands beforehand will not produce them. Virek is the NPC who issues the hunt, and he stands on his own small islet just off the coast of Sacred Mountain.
Step 1: Leave Bay Island (the default spawn) by boat and keep heading left along the ocean. A waypoint pointing toward Virek's islet appears on the map as you approach Sacred Mountain.
Step 2: Dock at the small island and speak with Virek. Select the quest dialogue option to accept the Sacred Relic hunt. Only after this step will the three relics spawn at their island locations.

Sacred Relic island locations
Each relic is a large purple object, which makes it easy to spot once you are close. The island for each relic is fixed, but the precise spawn point on that island shifts between play sessions and between players.
| Relic | Island | Common spawn area |
|---|---|---|
| Sacred Relic 1 | Sea Stack Islands | Behind one of the tall stone pillars, often near the docks close to the Georgie NPC. |
| Sacred Relic 2 | Crescent Shore | On the grassy terrace ringing the beach, near where most of the island's NPCs stand. |
| Sacred Relic 3 | Bay Island | Anywhere on the island; often on a rock formation behind the Merchant's house or along the back beach. |
Sea Stack Islands is the closest stop to Virek, so it is the most efficient first pickup. Crescent Shore sits between Sea Stack and Bay Island on the route back, and Bay Island closes the loop at the spawn.
Sea Stack Islands relic
From Virek's islet, sail to the cluster of tall rocky pillars known as Sea Stack Islands. Run a quick lap around the main flat areas and check directly behind each stone pillar. The pillar nearest the docks, by Georgie, is the most reliable single spot to check first.

Crescent Shore relic
Sail to Crescent Shore and head onto the raised grassy terrace that wraps around the beach. The relic usually appears somewhere along that terrace, often within sight of the NPC vendors. If it is not on the grass, walk the beach line below before moving inland.

Bay Island relic
Return to Bay Island, the default spawn. The relic can appear in many spots here, so it pays to focus on two zones first. Check the rocks behind the Merchant's house, then sweep the back beach on the far side of the island. The purple coloring makes it visible from a distance once you are in the right area.

Turn in and unlock Sacred Mountain
After all three relics are in your inventory, sail back to Virek and hand them in through his dialogue. The reward is access to the Sacred Mountain island, which is a higher-level area intended for players who have already progressed past the starter zones.
You know the quest worked when Virek's dialogue completes, and Sacred Mountain becomes a usable destination. If you cannot land on Sacred Mountain, the most common reasons are that the quest was never accepted, that one of the three relics is still in the world, or that you have not actually returned to Virek to turn the set in.