As you might expect from a town that borders a massive marine and land National Park, Cassis is awash with diving schools. These include Cassis-Plongée (www.cassis-calanques-plongee.com) and Narval Plongée (www.narval-plongee.com). Novice divers may also scuba or snorkel along the Sentier Sous-Marin de Cassis, or underwater trail. This self-guided 30-min. swim route begins on the Promenade des Lombards. Four buoys mark marine life discovery spots along the way. Be aware that a mineral water source (as in thousands of bottles of chilled Evian) seeps from the limestone cliffs into Cassis harbor, so sea temperatures are often chilly!