Lille is dope as fuck and one of my favorite scenes in France, its history goes way back. Definitely lots of spots skated throughout the decades below the radar, a lot of which have come and gone, but some classic ones are still there (my favorite is Forum which has a shit ton of rough brick bubble banks, was partly skate stopped with little tube rails going across them the last time I went but poorly as you can now also skate those tubes). It's one of those cities where you just cruise and hit stuff up on the way though, nowadays the major hangout spot where people actually stick around for a bit seems to be the skatepark but honestly the street plaza thing they have is a ledge/stair skater paradise (I remember skating it back when it was brand new and completely graffiti free), then they have this massive indoor park just next to it but of the Disney World type with ten feet tall pyramids and a mandatory helmet rule so unless you're into that stuff and willing to pay for a miniramp sesh on a rainy day, that's better off as a more dormant option.
The city basically looks like this now, cruise and go style.
Also some super old stuff the locals have up, for curiosity's sake (again, classic spots such as that brick plaza are gone):
Have fun there!