Being in Nice you must visit the Promenade des Anglais. It is located just next to the beach and is a wide, lively and very busy sidewalk (7 km long) along the Mediterranean Sea. It is a beautiful place to watch walking people because it is full of them jogging, bicycling, skateboarding... There are covered places that offer lots of shade and seating so that you can very comfortably sit and just relax. Lots of bars, restaurants, activities.
The beach itself is very beautiful and the water is so blue that it cannot be described by words. We filmed it in our video but in real world the water is even more beautiful. Remember - it's not a normal beach: there is no sand yet only little rocks, so if you want to walk along the seaside with bare feet it can be a little bit dangerous for them. You may of course simply sunbathing on the beach, swim a pontoon or float in the air with a parachute pulled by a speedboat.
There are many interesting buildings on the Promenade des Anglais, for example Palais de la Méditerranée (A; GPS: 43.695208, 7.263015), Casino Ruhl (B; GPS: 43.695408, 7.265717) with the Hotel Le Méridien and famous Hotel Negresco (C; GPS: 43.694634, 7.258266) located nearby the Massena Museum (D; GPS: 43.695207, 7.258901). Very close to Promenade des Anglais you will also find the beautiful old town of Nice.