The Jalsavrah Pyramid, simply known as Plunder Pyramid, or Sophanem Pyramid is the location of the Pyramid Plunder activity.
There are four entrances around the pyramid, each decorated. Three are empty, and one has the Guardian Mummy inside of it, after speaking to him the Pyramid Plunder mini-game will begin. The door which leads to said mummy does change every now and then, however.
This Pyramid also holds the elusive Pharaoh's sceptre, which is a rare reward from looting the Pyramid.
Inside, there are 8 chambers which the Mummy allows you in: each dependent on your Thieving level. In each chamber, there is one Sarchophagus.
The fastest way to get to the pyramid, and Sophanem is the teleport function of the Pharaoh's sceptre. The next fastest way is teleporting to Al-Kharid, via Glory Amulet or Duelling Ring and get the Magic Carpet to Pollnivneach and then down to Sophanem.