Lille is indeed not directly a tourist destination, but you have to remain nevertheless carefull about your belongings and personal safety. How, discuss that preferable with the locals you will certainly meet. Susan´s remark ‘Walk with a purpose’ is a good one (that´s what locals do) and that´s the best way to avoid those you don´t want to deal with to my opinion. During your stay there will be anyway enough time to enjoy the sites.
In Lille you can visit the birthplace of Charles de Gaulle and Palais des Beaux-Arts. There is also a recently opened branch of the Louvre museum in nearby Lens. Some 30 km east of Lille in Belgium Tournai is a nice historical place to visit and totally not touristic. It has a small but nice Beaux-Arts museum and a lovely town square and cathedral, however the interior is under restoration.
More east of Tournai there is Chateau de Beloeil and theme park Pairi Daiza. As Le Cateau-Cambrésis is the birthplace of Henri Matisse, you can visit Musée Matisse.
Visit the lovely town squares of Arras and there is if it´s of interest enough to see in the area about WWI and II.