In this article, we present issues arising from Terrestrial Laser Scanning of large natural caves using the example of Skocjan Caves, a UNESCO World Heritage Site. Regarding pre-existing tachymetric survey of the passages and volumes calculated from them, the scanning of such a large cave was an even bigger challenge for the team. The cave of almost 6 km longpassages with dimensions approx. 30 m x 40 m and max. heights up to 145 m, was scanned from 370 stations. Process of surveying the cave, involves establishing scanner positions through the cave, where scans will overlap, in a progressive route and once back on the surface, collecting, cleaning and stitching the scans into a point cloud 3d ModeL3D model. A total of 8.3 billion points were captured and2,600high-resolution photos taken. With Reigls RiSCAN Pro software, a point cloud model was registered and then exported to Hexagons 3D Reshaper to create a full surface model from which all measurements and calculations were made. Additionally, data acquisition using a camera on an unmanned airborne vehicle was used. By photogrammetric approach, digital terrain model of a surface was built and then tied to the cave model within 3D Reshaper. The resulting high resolution - point cloud model may be used for various purposes such as: volume calculations, detection of geological andspeleogenetical features, etc. With a volume of 2.55 million cubic metres, Martels Chamber is confirmed to be the 11th largest cave chamber in the world at the moment.KEY WORDSTerrestrial Laser Scanning, point cloud, large caves, volume, Slovenia