Where are the "unofficial" entrances to the paris catacombs?

Question

and how do you access them?

Answer 1

I'm not going to post it on the internet. 

Chances are, if you're asking, you don't know anyone who actually goes down there and knows how to navigate it. Having been down there a few times with experienced people, I'm going to say DO NOT attempt to go down there by yourself your first time. It is a labyrinth - and an elaborate one - that spans around 100 miles underground. It is extremely dangerous if you don't know what you're doing, and even then, there is still a considerable risk of injury or getting lost.