Pokémon Diamond and Pearl/Solaceon Ruins

Solaceon Ruins
Slighty to the east of Solaceon Town, the ruins contain the infamous Unown, a type of Pokémon needed to be seen here for the PokéDex since there are no trainers with any. There are Unown A-Z and after talking to the Ruin Manic while having one in your party, Unown ! and Unown ? are able to be caught through the hole in the wall.

There are also some items scattered throughout.