The party carefully descends into the bug hole, with Andrej in front. His infravision, separated from the torch, allows him a vague view of the tunnel perpetrated by the heat produced by the thin plant covering, lichen that is in fact too small to be seen. Andrej recognizes this effect, however, and realizes that if not for this spore-level life, it would be too cold for him to see at all. As it is, he can only barely discern the tunnel's shape. Slowly, from the torch light above, his light-detection faculties take over, and he can see a tunnel that slowly curves to the left and out of sight, some 30 feet away.
Presuming, if I may, that the party decides to continue forward for a minute, or five rounds, moving carefully, only 10 feet per round, they follow along the tunnel for fifty feet from the Old Storeroom. The tunnel descends slightly, and weaves in a gentle path away from where the river bottom of the valley would be, somewhere to the party's right (right and behind, as they follow the passage forward). The descent is between five and ten degrees at most. Andrej is forced to either light a torch or take the one from the back of the party, as his own shadow is blocking his clear vision of the way ahead.
I'll pause there, to let the party decide on further action.