The upper-right entrance 1, near the Route 36 entrance, requires no HM moves to access. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads "escape" upon inspection. Using an Escape Rope there opens a hidden room. The chamber's puzzle forms an image of Kabuto.
The lower-right entrance 1 requires Surf to cross the pond on the south side of the ruins. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads "light". Using Flash will open the hidden room. The chamber's puzzle forms an image of Aerodactyl.
The upper-left entrance 1 is accessible only from the basement of Union Cave, which requires Surf to navigate. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads "Ho Oh". The hidden room will open if Ho-Oh is...anywhere in the player's party in Generation IV. The chamber's puzzle forms an image of Ho-Oh.
The lower-left entrance 1 is accessible only by moving a boulder in the basement of Union Cave, which requires Surf to navigate as well as Strength. In Pokémon Crystal, HeartGold, and SoulSilver, the far wall reads "water"...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. The chamber's puzzle forms an image of Omanyte.
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First is Kabuto, others are Aerodactyl, Omanyte and HO-OH
