One of the neat things about the old Middle Earth Roleplaying Game (MERP) and Rolemaster was that characters gained experience points for every mile traveled. This was even calculated by whether they were going down a road or through wilderness (with rough travel granting more experience). I always liked this idea.
Sadly, it has never really caught on in gaming, and in fact, has been removed from the later editions of Rolemaster. Considering just how much stuff you have to do in order to travel through a hilly forested area without roads, I would love to see it added into people's games.
Maybe something as simple as an extra 50 xp for traveling through wilderness for one day. It doesn't have to be a huge amount, but a little bit helps encourage the whole exploration aspect of gaming.