This is an amazing card for those scenarios that feature lots of locations with nasty (travel) effects. Don't make the mistake I did in thinking it's a one-off effect: the player stays in control of the card when it's attached to a location (see also section 1.38 of the FAQ). That means that you can decide to use it's Response again at a later time, for example, after having travelled to a location and skipped its effect. The only restriction is the availability of other locations (and the proper use of the Action Windows).

Indeed, this key opens many doors!

A really amazing attachment, especially at high player counts where seeing lots of locations is quite common and there are some brutal one, from X where X is the number of allies/characters controlled by the first player", to anti-Northern Tracker ones, to those which block canceling encounter effects and so forth. It saved our asses a few times and I always try to include it in a Spirit deck of a 4 players Fellowship.

Thrór's Key gets my vote for favorite location attachment. If this card is 1) not already in play (unique) and 2) is attached to one of your heroes, you can attach this to any non-immune location that is added to the staging area (not just revealed). Think of all the evil things you can cancel - travel effects, passive effects, variable values - the list is extensive. Dwarven Tomb and other cards can recycle Thrór's Key after it's discarded. In a quest with nasty locations with nasty effects, why wouldn't you include this key attachment? P.S. This card can only be attached after the location is revealed so surge and when revealed are not canceled.