Some quest or places have portals.

Is it possible to have some kind of lore-check or spellcraft-check to have an idea of the destination? Or perhaps some clue (book, carving, etc.) to find IG (perhaps there is actually, but i never found any).

I'm thinking in particular of the portal to -spoiler- on the Clan Duergar quest, and the Seer's quest as well.

What are the comments on that?

I like this idea. A double, spellcraft / lore roll maybe (you have to pass both)?

Indeed, otherwise the decision to jump through a random portal you find could be hard to find reason to IC, while it creates a hella lot of hassle -not- to do it.

Please note that any portal you encounter leads to the surface.

This won't happen.