Beyond tracking and survival I could sure appreciate some brainstorming around good ideas for skill challenges using Nature.
Ability to add in Diplomacy, Bluff, Religion, History and Arcana are pluses
[RPG] Need skill challenge ideas for Nature
dnd-4eskill-challenge
Related Solutions
Making it engaging, and definitely unique, is a way to make it memorable. I'm afraid I can't be more specific; usually it's how the players handle them that make them unique. Even the most mundane of challenges are exciting and rewarding if something off-the-wall or otherwise impressive happens - especially if they roll a 1 or a 20 and you use critical successes for skillchecks.
To give an example, my current game had a player try to chat up an NPC for information, using a simple Diplomacy check. The party eventually succeeded, but the initiating character had rolled a 1, and ended up falling off his bar stool. Considering the fact that he was trying to impress the NPC - an attractive woman - it made for weeks worth of teasing for the entire party.
Alternately, you could throw in skill challenges during combat. An example is from the Tomb of Horrors supplement, where a skill challenge involves trying to disable a magical ward/device while defending yourself from an onslaught. The goal is to disable the ward and escape, not to defeat the enemies, and the experience is all the more harrowing for it.
The only other advice I could give is to make the challenge open-ended, which allows for more creativity from the players in overcoming the challenge. If they come up with off-the-wall solutions for their rolls - like using Acrobatics to wall-jump up a narrow hallway to disable a fire alarm at the top, or something equally impressive - they will remember the challenge for years.
The religion skill in Dark Sun is not useless if you look at it from a different angle.
History is a more generalized skill so it is less likely that you would have a character that studied history know about the old religious objects that are still around even though the gods are not.
Ex. the party is in a dungeon that a use to be a temple to [insert god here] and have come to a door that is only activated by answering specific questions about the deity or how that religion viewed history, this would make the history check for the challenge much harder then a religion check.
There are other ways to use the religion skill as a main skill in challenges or for interpreting religious texts on the walls of old tombs and such to help get to or around things. Remember that just because the gods are gone now does not mean they were never there. Religious cults and peoples are known for their odd ways, intricate religious objects, and mysterious places.
That is just my take on the matter bass line is that you are the DM do what you feel is best for your campaign and group. A final thought if one of your players has taken the religion skill try to let him use it every so often to make him or her feel like they didn't waste a skill slot.
Best Answer
Here's a few:
Nature: Characters stumble out of one heavily overgrown area into an open area where a large beast (grizzly bear?) and her cubs are drinking. players could use nature to calm the beast and backtrack out of the area.
Diplomacy (or bluff?): players have accidentally wandered into a dryad's grove (or done something else offensive), and she has been spending the last hour of travel shadowing the PCs and making the trees fwap them in the face and run them in circles. Eventually she appears, flanked by a pair of treants. Players will have to talk their way out of this situation.
Bluff (or Diplomacy): players run across a pair of satyrs who have charmed an owlbear and are holding a music contest to see who can make the owlbear dance better. Players are called upon to take partin the contest as judges and participants, and of course, if the satyrs get offended, they'll unleash the owlbear.
History: Characters stumble onto an ancient monument (written in elven or even giant), overgrown with trees and scrub. A history check gives them a general sense of where they are in the forest.
Arcana: the spider-webs of a group of monstrous tree-dwelling spiders have been woven into complex and mystifying patterns. An arcana check will show characters a "shortcut" through the feywild outlined by the webs as way-markers. A failed arcana check will strand them there, for a time, near where a hag stalks the woods.