The trail through the forest meanders a bit, but is relatively easy to follow for anyone with rudimentary knowledge of trails or outdoor survival.
You can have the party roll mental, but the roll only determines how difficult they find following the trail, it is obvious enough that even with a bad outcome they will eventually find:
At the end of the trail, the party finds it going into a cave. The terrain is a bit rocky here, but the cave entrance is a surprise anyway as there are some hills around, but no mountains.
The entrance is low and characters will have to bend low or rob into it. It is wide enough to allow anyone in, even those with heavy armour and long weapons, and after a few metres crawling slightly downwards, it opens up a bit more to standing headroom.