Rescue Zandalor (Rivertown sewers castle entrance) and let him bring you to a new area to get the teleporter stones back (after clearing the location).
The lanterns are the intended way to get into Dr Elrath's cellar. The teleporter pyramid trick is useful if you don't find everything you need in the cellar before you leave (after that, the house gets locked, and there is no way to open the front door again).
