In Gruet Cave, there's a unique hydrological phenomenon influenced by the melting glacier above the Apuseni Mountains. The cave's internal river system is fed by this glacial melt. However, when it rains, the cave rapidly fills with water, flushing out the colder glacial currents. As a result, the cave's temperature doesn't remain as frigid as one would expect with only glacial water. This creates a more balanced and less extreme internal climate, adding another layer of fascination to this already captivating underground world.

Because of the unique blend of glacial and rainwater in Gruet Cave, the temperature inside is more moderate than in purely glacial caves. This makes it an ideal habitat for bats, which are the primary residents of the cave. Unlike in other caves, where bats may only inhabit the entrance, in Gruet Cave they are found throughout its length, up to the central chamber. This offers a fascinating insight into how hydrological and climatic conditions in a cave can impact its ecosystem.

Bats are often shrouded in myths and legends. In some cultures, they're associated with vampires and considered harbingers of evil or death. However, most of these beliefs are largely unfounded and do a disservice to these fascinating creatures. In reality, bats play a crucial role in ecosystems, helping to control insect populations and even aiding in pollination. They're far from the menacing figures of folklore; rather, they're highly specialized mammals that have adapted remarkably well to their environments. Contrary to the common myth that bats are blind, many species actually have good vision. The vast majority of bats are also not harmful to humans and prefer to keep to themselves. Overall, the mysterious reputation bats have garnered through folklore is largely undeserved, and these creatures are far more beneficial to us and the environment than they are given credit for.