If you want to get all 28 kinds of unown, here's what you do:
Run aroun in EVERY SINGLE chamber in Solacean ruins (near slocean town). catch at least 10 different types. go into a cave a little south of Veilstone city. talk to a guy a t the end.(theres pokemon in there that you cant get anywhere else: hippopotas) go back to Solacean ruins and catch ALL the letters of unown. then go back to that other cave and talk to the guy and he'll say he dug into a weird place. go into that weird place and catch the last two types of unown.