Deep beneath southern Europe there stretches a 500 kilometre long subterranean world. Underground rivers and vast caverns are home to unique and unusual species like the blind salamander and the freshwater sponge. Barely explored, the caves of Italy, Slovenia, Croatia, Bosnia and Albania are facing up to a rash of environmental threats.

In Costing the Earth Tom Heap will be joining caver and Whitley Award-winning biologist, Jana Bedek to explore the caves, spot the wildlife and witness the destruction. Waste dumping and agricultural pollution are damaging waterways all through the cave system but it's in Croatia that some of the toughest challenges exist. Preparing for European Union membership the country is pushing ahead with the development of highways and hydro-electric plants. The construction is threatening some of the most valuable wildlife sites on the continent but the damage is invisible to most local people and all but the most adventurous of visitors.

Is damage unavoidable in the rush to join the EU or does Croatia risk losing its natural foundations?