I invite you to go to see these remarkable buildings that are really close. First, the Porte de Paris is impressive because of its height and the little garden in the center. Its history is interesting, it was built by Louis XIV in order to ensure the strength and the power of the royalty after taking back Lille to the Spanish Holland.
Concerning the Hôtel de Ville and his beffroi, it is a beautiful monument and what worths it is to go on the top of the Beffroi to admire a good view of Lille !
PS: you can see a 2CV in front of the Porte de Paris, it is a great way to visit Lille to admire the buildings from the convertible-top !