It is special because it is active, in the Budapest under the sea, a lot of caves. Seven big caves and three dozen smaller one(s). Together is 40 kilometers long. Sometimes it's very beautiful precipitations: gypsum, aragonite, calcite, baryte crystals. But all the other cave(s) are inactive and dry.
Budapest has built above the maze of the largely unexplored caves, filled with hot thermal water. The heat from that water helps heat the Turkish baths. The government plans to allow the researchers full access to the site prior to making any major decisions about public access and officials are planning to apply to have the cave system declared as a UNESCO World Heritage Site.