That depends on which one you did fourth. You can do them all in different orders. It may be the Aerodactyl puzzle.
in the cave!
Yes if you complete a puzzle in one of the buidings you go underground you can find UNOWN and capture them and if you speak to one of the people aboveground they will give you an UNOWN Report to regisster the types of UNOWN in.
hidden power
you have to bring arceus to the unown house
Nothing happens if the unown you catch can be arranged to spell water.
nothng happens
To be able to find more unown!
in Pokemon heartgold ruins of alph in Pokemon soulsilver ruins of alph
Go into the tanoby chambers to catch the Pokemon unown.
Tanoby Ruins is the main location for catching Unown in Pokemon LeafGreen. To get the Unown to appear in the ruins you need to complete the Tanoby Key puzzle.
First go to the Ruins of Alph then go to the first puzzle room then try to complete it if you do then you will fall to the big room then the Unown will appear.
If you finish the puzzle you can catch the Pokemon unown in the tanoby chambers.