The constant temperature of the cave, will allow you to benefit from optimum climatic conditions in winter and/or summer; its underground setup will protect you from the elements.
The Fontrabiouse cave is a living cave (in constant formation). According to seasonal changes the cave will show a variety of faces. In periods of sustained rain the water runoffs will be stronger , the atmosphere would then become more humid, but this will not hinder your visit. However during the summer season (July and August) the cave will show you its thousands of facets, the decline of the water runoffs will give way to the natural sparkling of calcite crystals.