Fangorn Forest
"Fangorn. What madness drove them in there?"
Gimli
Fangorn Forest is huge beyond belief, with hundreds and hundreds or gnarled and bent trees. The ground is littered with leaf debri and massive roots, just waiting to reach out and trip an unsuspecting traveller. Overhead the trees seem to talk to each other, low rumblings and creakings can be heard and leaves rustle without the aide of the wind.
Merry and Pippin have no choice but to enter the vast forest. If they remain outside they will almost certainly be mistaken for Uruks and slain by the riders or else trampled by their horses. So they hurry on into the Forest in a desperate attempt for safety.
Fangorn Forest was once much bigger than it is as Merry and Pippin see it, however Saruman has been using the trees to fuel his machinery in Isengard. Once he would walk freely in the woods, now he sends his Orc servants to destroy it.
As Merry and Pippin hurry through the deep, dark undergrowth the sounds of battle can still be heard behind them, in fact some of the Uruk-hai have had the same idea as them and are also trying to fight their way into the trees. Although the hobbits don't stop to watch they might be pleased, or unnerved, to see that the trees almost appeared to be fighting back.