Thror's Key:

"Response: After a location is added to the staging area, attach Thror's Key to that location. While attached to a location, Thror's Key gains: 'Treat attached location's printed text box as blank, except for traits.'"

Ancient Causeway from The Lost Realm's "The Weather Hills" scenario:

"When Ancient Causeway is explored, raise each player's threat by 2."

So the question: some locations, like Ancient Causeway, trigger an effect once they are explored. This means they have been discarded from play and Thror's Key is no longer attached-- so maybe the text box is no longer blanked out. Will such an effect trigger, or does Thror's Key prevent it?

As exploring locations make you discard them immediately, alongside with their attachments, i would say that Thror's Key response still is active when the location is explored.

So, for me (without having any backup on previous ruling), i would say that the Forced effect of Ancient Causeway does not apply because its text is blank due to Thror's Key and only become "visible" again when the card is already at the discard pile, where, normally, it doesn't affect play because it is out of play...

My thought only...

I think it the same as when it leaves play, meaning Thror's key Edit: doesn't work against it.

Q: If we play Thror Key on a Warg Lair, can we draw cards when the location is explored?
A: Thror's Key works differently from Ancient Mathom. Thror's Key creates a constant effect that doesn't end until after the attached location is discarded whereas Ancient Mathom has a Response effect that triggers after the attached location leaves play. If you attached Thror's Key to Warg Lair, its only effect would be to prevent you from drawing a card when Warg Lair left play.
(French)

I think it the same as when it leaves play, meaning Thror's key doesn't work against it.

alogos, do you mean to say that Thror's Key DOES work against it? If it blanks out and prevents the card draw from Warg's Lair, would it not also blank out and prevent the threat raise from Ancient Causeway?

Oh... yeah, I didn't read that answer right (and it was my question to begin with)... ><

So yes, it should work.

Thanks for the help as always everyone!