Falco has gone off into the uncivilized (non-Roman-controlled) regions of Germany to try to speak with a witch/priestess who apparently lives in a forest, as well as to try to find a German rebel leader. They're leaving marshland and heading into the forest.
Next day we began to encounter stretches of light woodland, and at nightfall we hit the real edge of the forest. From now on we would need all our skills to find paths and keep to the right direction. From here the tree cover continued unbroken across the whole of Europe.
This counts as a forest for the "In the dark, dark woods" square, right?