The Jenolan Caves of New South Wales are Australia's most visited caves, and their tours cater to all kinds.
With up to 200,000 visitors a year, people are boldly going where many have gone before. Just to make sure their bases are covered, they offer self guided tours in 13 languages - and just to make sure their bases are REALLY covered, they offer tours of one of their caves in the debatably fictional language of Klingon.
The Star Trek aliens are a humanoid warrior race and have one of the most fully developed fabricated languages. With thousands of speakers worldwide there's a translation of Hamlet into Klingon and even a Klingon Language Institute with registered members, about 2500 of them.
Star Trek started the relationship with the caves, naming one of the starships in Star Trek: The Next Generation the “USS Jenolan.” While looking at new languages for the self-guided tours, it was decided to include Klingon and pay tribute back to the show. They brought in Klingon scholars and announced the tours at an Australian sci-fi convention in 2010.
Nettle Cave is the most visited caves in Australia that is open for casual exploration, where digital self-guided tours lead visitors around the ancient hole in the ground. Nettle Cave offers a variety of interesting sites, including Sooty Owls and stromatolites (structures made of sediment and cyanobacteria). The Jenolan Caves are some of the oldest caves in the world, estimated at 340 million years, and have over 40 km of underground passageways. While some of it is still being explored, there's currently no intelligent life down there.
Of note is the Vulcan State Forest nearby.