The object of the project was to replace a small and unsuitable human fish pool at the Postojna Cave with a new aquarium that would ensure suitable conditions for keeping human fish (Proteus anguinus) available for public viewing. As the Postojna Cave attracts up to 5000 visitors per day, it was necessary to design an aquarium that would bring one of the main attractions of the Karst underworld closer to larger groups of visitors, making use of the existing artificial berm and the widened area of the path through the cave.

Reflecting the flow of visitors, the structure design is in line with a request for large transparent glass surfaces and an excellent view of the aquarium interior for as many simultaneous visitors as possible while maintaining suitable conditions for animals. The size of the structure depends on enabling an optimal direct view and experience of the life of human fish as well as on providing sensitive animals with maximum protection from external influences. The structure was designed in close cooperation with a biologist and aquarium expert, observing strict conditions set by the Institute for Nature Conservation and the Environmental Agency of the Republic of Slovenia. Moreover, the project was a precedent for similar interventions in the cave.

The geometry of circulation paths, structure dimensions and its materiality explicitly separate the structure from its surroundings and make it a part of the path, a part of human intervention in the cave.

The foundation and base are made of concrete. The framework structure is made of steel, structurally separated from the aquarium and laden with Swisspearl fibre cement panels and a sheet metal lattice roof that lets dripping water through. The aquarium part is made of stainless steel frames and glass, while the service part, which includes lighting generators, a microphone, filters and pumps, is laden with sanded stainless steel panels. When developing the design, it was necessary to consider manual construction and accordingly adjust the size of individual elements, which can be transported into the cave by the cave train.

The spatial design adapts to the current access axis of the path through the cave. The front of the aquarium functions as a screen that is perpendicular to the path, announcing the attraction from the distance. The facade lines reflect the path inclination and thus contribute to the dynamics of perceiving the size and dimensions of the structure.

The structure design meets the requirements for providing a favourable habitat for human fish (Proteus anguinus): using cave dripping water from the current collector, optical fibre illumination without harmful radiation turned on only when a group comes by, etc., and inorganic materials.

The spatial design is adapted to the flow of visitors, who gather around the aquarium and then continue their path through the cave.