If you solve all 4 puzzles it will unlock the 26 "letter" unown. If you open the 4 back rooms (using an escape rope, flash, water stone, and Ho-Oh), catch all 26 unown, and talk to the researcher in the building it will unlock the ! and ? unown. Catch them and talk to the guy again. This will complete the unown side quest, but that's about it. Nothing really special unless you just really have to have all 28 unown.
Chat with our AI personalities
The tunnel on top the ruins is accessible.The tunnel is where you catch the ? and ! Unown.
Nothing happens, except the fact that you have many Unowns. ~Katie
If you catch 26 Unown in Pokemon Diamond, go to Ruin Maniac Cave. He will be waiting inside for you. You can catch Hippopatos in the cave, along with Geodude. Go to the end of the cave where there is another entrance. Go through, and when you get inside, you will see a writing on the wall. It says, "?!" Those two Unown are in there. Capture them. You now have all the Unown.
nothng happens
The only thing to do in the tanoby chambers is catch the Pokemon Unown.