Complex sentence: As an adult, Gadal worked as a schoolteacher but his fascination with the Cathars lead him to work for the Tourist Board Of Ussat Ornolac which saw him exploring the Pyrenean caves which he believed were hiding places and sites of worship for the Cathars.
Split into simpler sentences: As an adult, Gadal worked as a schoolteacher but his fascination with the Cathars lead him to work for the Tourist Board Of Ussat Ornolac. In doing so he was able to explore the Pyrenean caves himself, which he believed were hiding places and sites of worship for the Cathars.