One of the best things to do in Paris is simply wander to see what awaits you around the corner, and just around the corner and across the footbridge from Notre Dame, on the Ile St. Louis, (31, Rue St Louis en l'ile to be precise) you will find what is reputed to be the best ice cream in the city at Berthillon's. Rumor has it the ice cream is divine at any time of year!