This ancient Slate Pyramid has 50 levels inside. While inside the pyramid, your pet will see ancient symbols on the walls or floor which will help him safely proceed to the next level. But you will need Simerian Slates to help translate.
At each level of the Pyramid, you will get a prize. It can be either items, currency, pet stats or Account Upgrade Credit. There is no time limit for completing the Pyramid, but you can only complete one level every 8 hours. If you manage to reach level 50, you will be able to change your pet into a restricted pet Echlin. Here is the Prize List.