Go to a tower in Vunkerl Inlet (S) at (D-11) and click on the ???. (The ??? is on the back side on a boarded up window ON the tower.)
Watch out for bombs!! (NOTE: It is possible to get out of this area without bomb aggro, but it's terribly difficult. There's not a lot of room to avoid aggro, and the bombs will magic aggro from quite a distance. If you're a mage, bring Prism Powders, as you won't be able to rely on Invisible.)
When you check the ???, the seal will be "lost".
Solo note: If you are soloing this quest and the ??? is surrounded by bombs (which it is likely to be), just do your best to examine the ??? as soon as possible. If you get aggro, examining the ??? should freeze the bombs in their tracks, and they will not continue after you lose the seal. However, the remaining bombs that have not seen you yet will still attack you once they find you.