if you head out north from the city on the road past Kampung Gajah and keep on through Parompong you will eventually come to a camping and activity area. Go up the hill past this and on the left you will see a suitable place for a walk from hell. I forgot the name - will have a look around and see if I can find it.
You can walk down to the bottom of the gorge there and the scenery is beautiful. Sadly for me on the day that I visited they had closed it off because all of the monkeys had come down from the trees and they thought it was unsafe for visitors- to be honest-I was quite glad... hehehe walking down would have been fun- walking back up might have taken me some time.