Those lights lead you to the portal to The Land That ime Forgot. Since you have already been there (via the mountains)
and, prresumably, have an LB set there, you don't need to find that portal inside the pyramid.Make sure you have set an LB outside the pyramid (anywhere in Baal's Garden is OK). What you should do now is find the money ($20 Mil or so) and then find the training hall (outside the Pyramid). You should level up for the HP and SP if nothing else as you will need them for the finl battle.
Once you have levelled up (you should be at least level 250), go pack to you LB in the Land That Time Forgot and find the Corrupted Chalice. The once the Chalice is in inventory, beacon back to Baal's Garden and all H#$L will break loose. You ill be glad you got those extra Hit/spell points . . trust me! 
