Make featured image link to post from gallery

I’m stumped. I’ve got this site:
http://nwrdev.mambomedia.com/portfolio/ and on the portfolio pages it’s pulling posts into a gallery (sorted by category). My problem comes in when I need to click on the main image to go to the post associated with that image to see all the info about that product.
I’ve tried quite a few suggestions I’ve found on the forums for other people’s problems that are similar, and I think it would work if it was just a series of thumbnails.
How do I get the main image to link to a post?