Given a travel related situation, and given a specific question about the situation, summarize the question into a title

I'd like to see the Catacombs of Paris in September 2017. It appears that tickets can be purchased in advance from http://b12-gat.apps.paris.fr/accueil.aspx ... is the demand such that purchasing tickets in advance is necessary if you want to see it?
catacombs of paris: should tickets be purchased in advance?