Tanoby RuinsFireRed&LeafGreen
"Ancient chambers on the southern tip of Seven Island. Solve the boulder puzzle at the Tanoby Key to cause Unown to appear inside each of the seven sealed chambers."
TANOBY RUINS MAP
Seven chambers spread across a chain of tiny islands south of Seven Island. Surf between each chamber. The Tanoby Key puzzle on Sevault Canyon unlocks them.
Pokemon Encounters
Unown at 100% in the grass, level 25. Outside the chambers, standard Sevii fishing applies with Qwilfish at 40% and Horsea at 40% on the Super Rod. Tentacool covers the surface.
Old Rod1
Good Rod3
Super Rod8
Magikarp
Also found in 41 other locations
ITEMS
A hidden Heart Scale near the chamber entrances. Limited practical use in FRLG, but a collector's pickup.
Heart Scale
A pretty, heart-shaped scale that is extremely rare. It glows faintly in the colors of a rainbow.
Heart Scale
A pretty, heart-shaped scale that is extremely rare. It glows faintly in the colors of a rainbow.
TRAINERS
A Gentleman, two Painters, and a Ruin Maniac scattered across the ruins. Varied teams near level 50 with no clear weakness to target.
Clifford
Tanoby Ruins Guide
Solve the sliding boulder puzzle inside Tanoby Key on Seven Island. Push all the boulders into the holes using Strength, and the seven chambers around the Tanoby Ruins become accessible. You need Surf to reach most chambers from the main Tanoby Ruins area.
Every chamber has Unown as the only walking encounter at 100% rate. Each chamber spawns different Unown letter forms. The chambers also have water, so Surfing and fishing encounters include Tentacool, Tentacruel, Horsea, Seadra, Psyduck, Qwilfish, and Gyarados.
Islands One through Three unlock after you beat Blaine on Cinnabar Island. Bill takes you there as part of the story. Islands Four through Seven require beating the Elite Four first, then completing Celio's Ruby and Sapphire quest on One Island to get the Rainbow Pass.
You can physically reach all seven islands without it, but evolved Johto Pokemon only show up in the wild after you get the National Dex. That means 60 or more Pokedex entries plus completing Celio's quest. If you're only seeing Kanto species, that's why.