A Look Ahead

Leaving the lizardfolk behind, the paths before you start climbing up across the hilly swampland. While the terrain is a mix of swampy areas and thermal pits, it is also a hillside. The difficult pockets of terrain serve to turn the sprawling, broken hillside into a maze. Navigating it successfully is slow going, even with a map offering a general direction.
Making the trek more challenging is the shift you notice as the hillside rises. What had been humid, dank and filled with the noise of bugs and critters, has become more arid with a reek that sickens the nostrils, and an eerie silence punctuated by the gurgling explosions of mud and lava erupting randomly all around you. It makes for a disorienting effect that is unsettling and nerve-wracking.

I've added a closeup of the map for the region ahead. There is still a good 40-50 miles to the slaad village, and another 50 miles beyond that to get clear of the mire. This central part of the quagmire is controlled by the slaad. They don't venture far west of their village, but they control the viscous wastes east of it for around 50 miles.
From there, it is about 100 miles to the entrance into the mountain, and the dragon's lair. By crossing the swamp, the party will be able to approach the mountain by way of kobold trails.
There is a kobold lair in the tunnels under the volcano, and somewhere between there and the swamp, the cultists' main shrine. The characters are on their own after the slaad village, but finding evidence of the shrine (which they already suspect exists) will be easy. The challenge there will be dealing with the kobolds without alerting them all or the dragon of the party's presence.