Underground natural caves are assets that present a tender and fragile ecosystem, usually containing not only the rocky part, but also mineral and hydra content, fauna, flora, archeological and paleontological sites. They are important from the environmental, cultural and economic points of view and constitute an impressive tourist appeal, because of the beauty of speleothems, of the underground rivers and lakes, waterfalls and historical vestiges. However, there are few law writings that aim to analyze the juridical nature of the asset. The scarce literature has been restricted to the analysis of the caves in relation to the preservation of their natural heritage, their cultural and even their economic value. This article aims to present a contribution to the analysis of the juridical nature of the asset, because very little has been written about it so far; even more specialized literature dealing with public or environmental assets has not been concerned with the cave study. Research developed here is bibliographical and exploratory and, to reach the goal, the doctrinal positions about the classification of the assets have been analysed, enhancing the main notes. The theories based on the asset titularity and the ones that adopt the juridical regime have been presented. Later, the main fundaments for the adoption of the two-fold and three-fold classifications were taken into account. On the basis of the legislation and of the normative acts related to the asset at issue, the similarities and differences between the possibilities of subsumptions have been studied. At last, the choice fell on a three-fold classification, supported by Silva (1997), that categorizes the assets into public, private and of public interest. The caves would thus fit into the last group because, although belonging to the Union, they have a system of rules that makes them different from the assets of common use, the assets of special use and the assets of dominical use. The difference is based on the necessity of a consistent system of rules expelled by the government with the objective of preserving the asset, which inhibits its use in a concurrent and indistinctive way by everybody, dispensing with previous authorization. Likewise, they cannot be characterized as assets of special use because they cannot be used as public buildings or be lent to render public service. They cannot fit into dominical asset either, because they are assets that have a purpose of public interest, and it is the State that has the obligation to preserve them. They are non-disposable assets and, even if it is possible the have a sustainable exploration by private ownership, tourism for example, the relation will be ruled by norms of public rather than private law.
Underground natural cave; Public interest asset; Public asset