For more than 17,000 years, the bestiary of the Lascaux cave in southwestern France survived the ravages of history, unseen and undiscovered. Entering it now is like walking into a time capsule, where 12-foot-long bulls and plump yellow horses appear to float across the vaults like religious apparitions. Although the draftsmanship is strikingly Modernist--on exiting the cave in 1940, Pablo Picasso is said to have remarked, "We have invented nothing"--these creations are remnants of the Upper Paleolithic Age, when our hunter-gatherer ancestors acquired the gift of consciousness and a knack for nature drawing.
This will be difficult to deal with, even once/if the fungus is eventually irradicated. One is tempted to just say "Seal it up and hope everyone forgets about it" but that probably can't be done, assuming the cave was not sealed up to begin with; that is, if the stuff inside survived inside an open (to whatever extent) cave, just sealing it up might cause more harm than good. But if you don't seal it up, people will continue to go in. I personally am not confident that anything can be done long-term -- i.e., thousands of years -- to preserve them apart from putting the condition of the cave back to where it was before it was discovered and finding some way to block access.
But it's a good article so read the whole thing.