I loved trekking in the Wadi Al Mujib Nature Reserve, but plan ahead and take spare shoes, a swimming costume and sun cream because three of the four paths offered alternate between passages of walking and swimming in the little river at the bottom of the gorge: it's quite sporty!
Only the Ibex Trail (which lasts 4 hours and stays up on the higher ground) can be done while staying completely dry. The departure time for this trail is in the morning, be prepared. As for me, I did the Siq Trail which was frankly quite hard but quite quick (a few hours).
A word of warning: it's closed from November to March as are the two other treks that have passages in the bottom of the gorge as the water is too cold. I was pleasantly surprised by this trek-canyoning experience: when alternating between passages of swimming and walking on the side of the cliff, the views are very impressive. A life jacket is provided.
My only regret is that you can't take a camera unless it's waterproof.