In summer, walking along the new pedestrian river banks on the Left Bank is difficult to skip while in Paris. Here, you can find an article about this pedestrian promenade which opened in 2013.
One of my favorite places along this path is Flow – Plage Ephémère, which is a bar and restaurant (burgers, salads) which gets really (too much according to me) crowded on sunny evenings for the apéro or dinner, but is much more relaxed during the afternoon, when you may want to have a good rest in the shade.
The place is basically made of three rows of beach chairs facing the river Seine, at one of its most picturesque sites: in front of Alexandre III bridge (generally considered the most beautiful of the 37 bridges in Paris) and the imposing glass roof of the Grand Palais. Some quiet relaxing music is displayed, not too loud, through suspended loudspeakers.
And finally, another really nice thing is that the staff of the bar does not harass you to buy drinks – you can stay quite long in your beach chair before a waiter comes to disturb you (actually, if you really want to buy a drink, you’d better go directly to the bar before laying down in the beach chair – otherwise it might be difficult to stand up again)!