They have been fighting the hobgoblins and Bane-ites on-and-off for the whole campaign, and have known for several levels that there is a fortress in the mountains. But not until this most recent session did they actually make their way there.
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the army encampment was much as the module describes it - an encampment of 500 or more, doing army things (eating, sleeping, drilling etc), and with a stairway up to a temple which is where the leader of the army, a fallen paladin, is to be found.
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they decided to use deception. The wizard PC had memorised Disguise Self for this purpose, and he also got around to filling one of his 15th levvel ritual slots, deciding that the Seeming ritual (from the Eberron book) seemed like a suitable choice.
The wizard Disguised himself as Paldemar, an evil wizard who had been a leader of/advisor to the army, and whom the PCs had recently killed, but who the army (as best they knew) didn't yet know was dead. He flew on the wizard's Flying Carpet (which the PCs had recovered from the wizard's tower after killing him) at the back of the procession.
The dwarf fighter had his hands loosely tied together with some copper wire that one of the PCs was carrying, and the Seeming turned that into shackles, with a chain being held by the party paladin, who Seemed to be a heavily armed-and-armoured wererat enforcer.
The other two PCs - a drow sorcerer and elf ranger-cleric - were changed to appear like wererat thugs. (The PCs had already learned that the wizard and his accomplices were using wererats as agents in the nearest large town south of the fortress.)
With the disguises established, the actual process of making their way across the encampment played out as a skill challenge - or, in fact, the final 4-check leg of a longer challenge (which involved other elements of navigating through the mountains), in which they had already accrued 8 successes and 1 failure.
The sorcerer started with a Streetwise check (aided by the paladin) to try and choose a suitable route through the tents etc where they would not be hassled or crowded (which could reveal their illusion). Unfortunately this failed, so just as they entered the tents in what seemed to be a low density area, a hobgoblin squad marched in front of them from behind a couple of tents. The quick-thinking paladin player responded by immediately barking orders at the hobgoblins, telling them to "Clear a path so that Paldamar can take his prisoner to the temple for interrogation" - and a successful Intimidate check resulted in a success.
As the procession moved through the encampment with the hobgoblin squad clearing a path, Bane-ite thugs who recognised the dwarf prisoner started approaching to throw mud and refuse at him. Not wanting any filth to reveal the illusion (eg by clinging to the fighter's halberd, which the illusion had rendered invisible), the wizard quickly cast them away with a Twist of Space, making sure that the rabble didn't further impede the procession's passage. (This also reinforced an Intimdate check from the sorcerer reiterating the need for unimpeded passage.)
Finally, the procession got to the foot of the temple stairs, where the two Bane-ite wardens asked for the password - which the PCs (and players) did not know. The paladin suggested Diplomatically that it would be sensible for everyone to let Paldemar through, so that he could deposit his prisoner and then rest, and the wardens agreed - and reiterated that all it would take was the password!
And then two actions happened simultaneously (the two players speaking over the top of one another): the dwarf "prisoner" made a break for freedom, charging one of the wardens and knocking him down and unconscious (a Bull Rush assisted by Rushing Cleats and, given the difference in capcity between the PC and the warden as well as the not-yet-in-combat mechanical context, one that I was happy to let knock the NPC unconscious as well as aside); and the wizard used Charm of the Dark Dream, possessing the warden (determined by a random roll to be the unconscious one, given the two PCs acted simultaneously) and hoping to quickly learn the password by reading his mind (a DC 30 Arcana check).
The ranger-cleric tried to do something at this point (Intimidate, maybe?) but failed the check, distracted by the fact that "Paldemar" had vanished. But he quickly reappeared - the Arcana check failed. The player had spent an Action Point to make sure that his spell hit its target: he gets +3 from Action Surge and the best of two rolls from his paragon path, and being a generous GM I let him have two rolls for his Arcana check also. He rolled a 4 and a 7, which with a +19 bonus was not enough, so he left the body of the unconscious warden without having learned the password.
But the sorcerer made a DC 30 Bluff check and led the paladin to grab the Dwarf (one on each side) and drag him up the stairs, while yelling "This is a dangerous prisoner, and we need to get him inside!" The wizard cast Glorious Presence (? 13th level Encounter power from Heroes of the Feywild) to push back the awed wardens and hobgoblin soldiers. In the circumstances, this was enough for the PCs to get inside the temple fortress while the NPCs dithered in confusion and dissaray.
In skill challenge terms, the inability to provide the password was a failed final check - leading to 3 failures - but with some mitigation of the failure by the quick thinking of the players (and their PCs) to somewhat cover for their inability to work around the password. That is, they successfully made it into the temple, but with their deceit likely to be discovered in short order, when the unconscious warden recovered consciousness and was able to report (1) that the dwarf who charged him felt like he was under an illusion concealing helmet, weapons etc, and (2) that someone/thing had temporarily possessed him and tried to read his mind.