Complex sentence: The aquarium-terrarium is geographically separated from the zoo, it is in the inner city in the middle-age cellar system, and was built in 1985, at the 25th anniversary of the establishment of the zoo.
Split into simpler sentences: The aquarium-terrarium is separate from the zoo, in the inner city located within the mediaeval cellar system. It was built in 1985, to celebrate the 25th anniversary of the zoo.