I read a specific fic about a year ago where Dean and Castiel were in Purgatory.  I think it was post-season six and Dean had to go to Purgatory to save Castiel.  I don't think Sam was there.

When Dean was in Purgatory, he got help from some past dead SPN characters, including Lenore and Madison.

I think it was posted on LJ to the deancastiel comm.

Sorry, I can't remember anything else.  I think Purgatory was this dark wood and Dean was running around trying not to get killed by monsters while he looked for Cas.  In the end he found him and they both got out.

This was definitely Dean/Cas, but I think it was pre-slash.

If anyone can help, I'd really appreciate it. I'm sure most of you can guess why I want to read it again!

FOUND: Hearts and Grace Entwined by Wolfing
Thanks to kestrel1966