As mentioned, Olms live in caves, exclusively underwater. Because they live in light-less environments, they lack most pigmentation in their skin, and they have essentially lost their sense of sight (their eyes are actually covered with skin and serve only as basic light sensors). To make up for the darkness, Olms have developed their other senses to an amazing degree. They are able to sense other organisms in the water using a chemical receptor in their taste buds. They are also able to detect different vibrations and sound waves, and even have a sensory organ that lets them register weak electric fields.
Olms have a few more relatively unique characteristics. One is that they remain suspended in a larval state for their entire lives. They retain large gills and a tail fin. The Olm also has a remarkably long lifespan for an amphibian. They might not reach sexual maturity until the age of 15, and individuals have reached 70 or older. They also reproduce externally, and the mother guards her eggs until hatching. The eggs are extremely dependent on the water temperature, and there is one hypothesis that females will hatch their eggs internally if the water is too cold.
Olms are extremely vulnerable to climate change, as their watery underground habitats are directly affected by what is going on on the surface. They are listed by IUCN as endangered.