From backside postcard:
Ruatapu cave meaning sacred cave also known as Aladdin's Cave descends steeply into volcanic tuff. Tuff is consolidated ash deposited from a volcanic eruption, this one being from an eruption approximately 100,000 years ago. The cave extends 45 metres into the surrounding rock and descends for 23 metres. The small pool at the base of the cave is known as Waiwhakaata or 'The Pool of Mirrors'.
The Maori people once used the pool at the base of Aladdin's Cave as a place to clean themselves.