Ruin Maniac Tunnel (Japanese: いせきマニアのあなRuin Maniac Hole) is a tunnel that leads between Route 214 and Solaceon Town via the Solaceon Ruins, though Solaceon Town itself is not fully accessible in this way.
The Ruin Maniac, when the player first encounters him, will propose a race: he will dig straight through the mountain as the player captures the different Unown. This race, of course, ends in a tie; after the player has captured the 26 Unown that are in the form of letters, the tunnel itself will extend straight through to the previously-inaccessible upper chamber of the ruins, where only the ? and ! forms of Unown are available.
As the player progressively catches the various forms of Unown, the cave will lengthen, and the availabilities of the Pokémon in the cave will alter.