if you already catch all of them (in different shapes) just keep them. there's nothing to do with them anymore i guess. it also became a puzzle to me what to do next. but after few a while i decided to keep them. but still you can try unlock few unown things which i don't know.
Yeah. I have settle with that. You open your pokedex then press select. Choose Unown mode. You look closely to that pokemon than you realize that one Unown will show one alphabet like 'a'. Just list them until 'z' then you can look the words in the ruins. The first word is escape. Thats the clue that I can give to you... (use escape rope then)