In Crystal, HeartGold, and SoulSilver, each puzzle chamber has a word on the far wall that is a hint to unlocking a secret room. When the player completes a certain criterion, the secret room opens, revealing several items. Additionally, in these games, completing the slide puzzles reveals part of the history of Unown written on the floor of the underground hall. In the Japanese version of Crystal, a scientist theorizes that the sudden appearance of these patterns is related to the newly-built Pokémon Communication Center and the radio waves emanating from it.
The upper-right entrance 1, near the Route 36 entrance, requires no HMs to access. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads escape upon inspection. Using an Escape Rope there opens a hidden room. In Crystal, the item is consumed and the player must re-enter the chamber in order to reach the hidden room. In HeartGold and SoulSilver, the item is not consumed and the room opens immediately.
This room contains a berry, PSNcureberry, heal powder, and energy powder.
The lower-right entrance 1 requires HM03 Surf to cross the pond on the south side of the ruins. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads light. Using HM05 Flash will open the hidden room.
This room contains a heal powder, energy root, gold berry, and moon stone.
The upper-left entrance 1 is accessible only from the basement of Union Cave, which requires HM03 Surf to navigate. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads Ho Oh. The hidden room will open if Ho-Oh is the first Pokémon in the player's party in Crystal, or anywhere in the player's party in Generation IV.
This room contains a revival herb, charcoal, gold berry, and mysteryberry.
The lower-left entrance 1 is accessible only by moving a boulder in the basement of Union Cave, which requires HM03 Surf to navigate as well as HM04 Strength. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads water. In Crystal, the hidden room will open if the player has a Water Stone in their inventory, and in HeartGold and SoulSilver, it will open when the player selects "Use" on a Water Stone from the Bag while facing the wall. This act will not consume the item.
This room contains a stardust, star piece, mysteryberry, and mystic water.
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