The Swamp

I wanted to provide some answers, but they aren't there. I could try to force something out, but that wouldn't work. I'm going to push on, and let the answers come later when my mind is in the right frame to provide them.
Leaving the monk's cabin, the journey back to the main trail seems to take mere minutes compared to the climb up, and if anyone glances back the way they came, there is no sign of cabin, monk or trail. They all appear to have vanished without trace. In truth, the monk was able to warp reality slightly to invite the party into an extraplanar space designed to fit in with their real surroundings.
Traveling west, the prominence of the volcano grows until it dominates the horizon before you. The last remnants of shrub fall away. The valley stretches out before you to the north, but the land revealed is unlike anything you have encountered elsewhere. There are long arms of rock and slag stretching out like snaking roots from the volcano itself, creating undulating valleys and large flat ledges stepping down away from the peak.
Oozing and seeping down, through and across this landscape is a foul, slow-moving sludge of lava mixed with water, earth and slime. This creates a nasty terrain that is tricky to navigate, with many swamp-like features. There are dead-end passages, oozing pools, and streams of slime everywhere. Coupled with the thermal veins running beneath the entire mountainside, erupting sporadically in plumes of steam or lava, the way forward is unpredictable.
With sinking hearts, the party looks out over the quagmire. They have little faith that their map holds any promise of value. Imogene steps forward with confidence and urges you to shrug off your hesitation and follow her lead. She insists that even though the terrain is open, there are definitely places to hide concealing watchers. You need to get out of sight quickly. She is also certain that the map is accurate and will be of use.
She has been studying it as much as she can, and believes that once you can locate the initial marker on the map, she can follow it from there. The trick will be finding the initial marker...