They can be found in the following arrondissements municipeux and each has information on them
5th, 6th, 12th,13th, 14th, 15th, 16th
They are originally abandoned quarries in three different networks (5th, 6th, 14th,15th then 12th then 16th), where gypsum was mined and are now the ossuaries for 6m people
Technically exploring the mines is not permitted and you can be fined but they are often explored by people called cataphiles. However the good news s that about 1.7kms of the mines have been granted a permit ie the ossuary part known as the Catacombes de Paris
They are just south of the Gate to Hell (one of the entries into Paris City) and can now be entered from Place Denfert-Rochereau, previously known as Place d'Enfer, a public square located in the 14th arrondissement of Paris, France, in the Montparnasse district, at the intersection of the boulevards Raspail, Arago, and Saint-Jacques, and the avenues René Coty, Général Leclerc, and Denfert-Rochereau[fr], as well as the streets Froidevaux, Victor-Considérant and de Grancey. It is one of the largest and most important squares on the left bank of the Seine.
The catacombs are known formally as l'Ossuaire Municipal or Catacombes officiels
I attach a map below from 1857 off wiki and have a map of the whole mines if you need it
Sorry for double post
If you zoom in to the map on the right hand side is some fascinating information when the tombs were discovered during building works at St Innocents which house building was stopped to allow an Inspection
The catacombs are called Ossements and marked on the map by letters from A to f
Even sorrier for the triple post - the catacombs are recent c1780 and were prompted when the St Innocents cemetry had to be renovated. Some 2m Parisien dead were relocated to the ossuaries as well as the cemetries at Saint-Étienne-des-Grès (one of the oldest), Madeleine Cemetery, Errancis Cemetery (used for the victims of the French Revolution), and Notre-Dame-des-Blancs-Manteaux.
Two much better maps