If you've never seen a Paris metro train packed to 175% capacity, strangers dancing against each other and riding on each other's shoulders, music blasting at a deafening volume, then you've never experienced an illegal metro party.
This particular party was scheduled for the same night as Paris's infamous Nuit Blanche, which is an all night celebration all over the city. The annual celebration features free art exhibits, light shows, and lots and lots of drinking. Nuit Blanche translates to white night. It's the French way of saying sleepless night, but the metro stops after 1 a.m., which means that unless you're willing to brave a long walk home, you'll probably peter out long before morning.