Ancient pyramids are the same as teleporter stones (except older <img src="/ubbthreads/images/graemlins/silly.gif" alt="" /> ). If you bring the teleporter stones with you to the wastelands, they get replaced by ancient pyramids in your inventory.
Morpheon; for your mana problem, make or buy a stack of
restoration potions.
Also, if you don't mind cheating a bit, there is a way to get back to Rivertown and pick up stuff;
Teleporting Anywhere, via hex editor
