In the previous session, the sorcerer PC had been
amassing chaos energy to try to infuse it into himself and/or items. This worked - he imbued himself with the Gift of Flame and also transmuted a jewelled horn the party was carrying into a Fire Horn. (Mechanically, this was resolved as an Arcana-based skill challenge while the rest of the party fought off the mooncalves who had been attracted by the chaotic forces.)
He also realised that, as well as the chaos energy leaking from the body of the dead dragon Calastryx (on which he was standing) and leaking from a nearby portal to the Elemental Chaos, there was elemental chaos flowing south from the mountains to the north. And as he stood in his chaotic vortex on the body of Calastryx, the apparent distance between him and the mountains closed, and he could sense the chaos leaching up from the underdark. And he could see a plateau surrounded by a ring of mountains, where an army of hobgoblins was encamped next to a temple to Torog cut into the mountainside - prompting the thought that the chaos energy was escaping because Torog had dug too deep into the world.
Now the PCs have for many levels been fighting against the hobgoblins, and the players have been planning to try and raid the army to the north, and so they decided to step through the vortex and cover the distance immediately, rather than have to spend a week or more climbing up through the mountains. They were a little concerned about arriving in the middle of the army - having only two or three healing surges across the whole party and two or three party members already being bloodied - and the player of the chaos sorcerer was getting ready to make more Arcana checks to try to shift the destination of his distance-spanning vortex.
But the wizard PC decided to use his Sceptre of Erathis (= 3 parts, so far, of the Rod of 7 Parts) to try and master the chaos - which (after a successful Religion check) resulted in the focus of the vortex shifting, to an ancient Nerathi stair at the bottom of the plateau, and at the base of a waterfall. (One property of the sceptre is its tendency to point out lost Nerathi paths and ruins.) So the PCs stepped through the vortex - taking 10 damage in the process, which most could not heal (and which left the ranger with 3 hp).
On the other side of the vortex, at the base of the stairs up the side of the waterfall, they took a short rest and then decided to look for somewhere to take an extended rest. They first spoke with the statues at the base of the stair (which I described by reference to the Argonath in LotR, only at the bottom rather than the top of a (more modest) waterfall) – I used the "dealing with the guardians" component of the running river (?) skill challenge in the DMG2 for this – and then climbed the stair to a ruined watchhouse on a bridge spanning the river at its top. And decided to rest there. (The stair, plateau, river etc are all from the old B/X module "Night's Dark Terror".)