Authorities in Germany have given the goahead for the world's largest indoor rainforest inside a giant structure outside Berlin, which was built as a hangar for 21st century dirigibles. The $75-million project envisions using the enormous hangar - the largest free-standing arched hall in the world - to house rainforest flora and fauna and six villages representing indigenous cultures in Malayasia, Thailand, the Congo, the Amazon, Bali and Polynesia.