 Over the centuries , the cathedral has suffered damage . A fire in 1967 destroyed a significant part of the cathedral 's interior . The restoration work that followed uncovered a number of important documents and artwork that had previously been hidden . Although a solid foundation was built for the cathedral , the soft clay soil it is built on has been a threat to its structural integrity . <unk> water tables and accelerated sinking caused the structure to be added to the World Monuments Fund list of the 100 Most Endangered Sites . Reconstruction work beginning in the 1990s stabilized the cathedral and it was removed from the endangered list in 2000 . 
