Resetting the Swamp

Having panicked, and let off some steam, we can continue with some clarification. The party is currently at the eastern edge of the quagmire, with a 200 mile trek through difficult terrain. After that, they will still be 100 miles from the dragon's lair at the volcano. The adventure is not nearly as close to completion as I was trying to force it.
With this cleared up, to have them emerge from the forest with a view across a barren stretch up the mountain is ludicrous. They are instead met with a despairing view across a seemingly endless landscape of wreck and ruin. The quagmire is a horrible mix of all the thermal elements that make Aron's Bowl an otherwise pleasant area in a hostile, northern mountain range. The thermal vents of lava and steam rise through swamp and ridge and earth to create a grim setting.
There are long ridges and spines of hardened lava running through the terrain like veins from the mountain peaks and volcanic ridge. There are tendrils of grass and forest threading their way up out of the plain of the valley like roots or branches of ivy looking for walls to climb. And the midst is a bubbling inferno of hot springs, stagnant, poisonous pools, and treacherous paths of crumbling earth.
The whole quagmire is like an open wound oozing and devouring the lower reaches of the mountains, and threatening to spread into the plain below. After gazing across it, the party can begin their journey by following the instructions on their map. The path cuts down into the steamy, molten mess, skirting pools and areas of quicksand and swamp, running up a ravine formed by a hollowed out lava tube. The scene described before with a stagnant pool and ravenous shambling mound occurs here.
After dealing with the shambling mound, the party continues into the bleakness of the terrain, while darkness begins to fall. They must find shelter in the nasty setting before dark. They are able to identify three potential spots - a sheltered clearing near a number of very small, foam covered pools (DC18 survival check to notice all the vegetation surrounding them is dead), a hollow opening about 15 feet above them in a cliffside that seems to run back into the cliff for several yards (DC16 survival or perception check to notice signs of passage by other creatures into the same area and opening), and a narrow shelf along an exposed ridge next to a constantly bubbling, oozing pool of heated mud running down the hillside (DC14 perception to notice a wider space just behind some thorn bushes that gives greater protection and cover).
If they choose the third option, they pass the night uneventfully. The first location is next to thermal vents that release poisonous gas every 3-4 hours, forcing everyone nearby to roll constitution saving throws against DC16 because of the gas. The effect causes 2d6 hp damage on a fail (half with a save), and the poisoned condition.
The second option places the characters in a small cave complex that is popular with multiple creatures of the swamp, which may move out (if already inside and not discovered), or in during the night. These can be chosen at random (I need to create a random monster encounter table for this area).