It’s actually very easy with ready-to-roll icing. Get a round cake that’s already iced in white. Blend some black and white ready roll to make grey. Put a strip around the base of the white-iced cake.
Add a second strip about an inch from the base and folded over so it is slightly extending into the centre. Pinch the edge of this to make it look like a straight-edged stone wall. Straighten the bottom edge of the upper layer with the blunt edge of a knife, pressing rather than cutting.
Add Eight evenly spaced 1 inch wide strips of icing vertically from the base and slightly extending into the centre. Again, pinch the edge to square it off.
Press some scrunched-up grease proof paper into the icing to give a stone effect. Use a sharp knife to score lines giving the brick effect.
There are hieroglyphics on the portal, so cut out the shapes with a sharp knife and fill them with white icing (I just used the ready roll stuff).
Finish off with a bright green, thin ribbon around the base and Skylanders game characters on the top.