In an attempt to avoid blatant spoilers, I'll only refer to this as the portal. Anyway, when I tell martin to open the portal, the two 'ingredients' disappear from the air and the ground lights up orange-ish but there's no clickable portal. I, at first, figured that I just needed to reload. I've reloaded from multiple saves and they all, essentially do the same thing.

Anyone know of a workaround (on the PC)?

Last I remember, the "portal" requires 4 "ingredients" to activate. Are you sure you far enough in MQ to open it?

I know the same thing has happened to some people before, but I'm not sure what causes it. IIRC, teleporting to Paradise using the console should be enough to get things moving again. The command is coc ParadisePlayerStart - always save first, just in case.