The Ankh is an offhand item found in Apmeken's tomb in the wall surrounding the Monkey colony after the Do No Evilquest. The cave can be entered by using the "Climb to exit" on a point near the top of the south wall. You will also find an Apmeken mask in the cave. In order to see the fissure you must have also completed the Diamond In The Rough quest.
Entering the tomb requires 80 Agility, rewarding 20,000 Agility experience when entering for the first time.(Note: exp boosts and double exp can be used to boost the exp reward.)