Off road travel through hazardous terrain should cost a cumulative X HP per day spent in that terrain. The X would be based on the terrain type and how hazardous it is, e.g. forest 1, swamp or desert 2, a Princess Bride Fireswamp 4, etc. So spending 4 days travelling in a normal forest would do you for 1 HP on day one, 2 on day two and finally 4 on day four. It's not a lot but that's just a forest- it would be pretty noticeable when spending a couple of weeks hacking your way through a swamp. Also I figure the Survival skill would negate this damage on a per point basis - so Survival score of 4 (a level 1 human hunter for example) would shield you for up to 4 points of this damage each day. Experienced survivalists (like high level hunters and druids) could stay out in the woods for very long times where a first level mage would probably die from exposure from a long weekend on the beach.
|Huzzah! An oasis!|
When that oasis comes into view over the sand dunes the weary travelers would indeed rejoice... that is until they discovered the terrible secret hidden within it's walls.