It only appeared when the moon was full and its rays illuminated the crag. Then there would appear a small and slender tower, glowing blue-gray as though it were constructed of tangible moonlight.
Adventurers were able to enter the tower and describe the interior. Inside, there were seven rooms and a rooftop floor. These were connected by a spiral stair of stone treads that floated without any visible means of support, and with no rail either. Magic spells cast within the Tower had unusual effects.
There were many different tales about what was found within. At times, the Tower was either empty or inhabited by rare or bizarre monsters; for example, an argos, or beholders, steel shadows, watchghosts, and strange, unknown creatures. Sometimes there was treasure, sometimes there was not. On occasion, explorers returned with a disease, eggs that hatched into dangerous monsters, or statuettes that reverted to living monsters.