The hike from the town of Cassis to the Calanques takes about 2 hours each way. The path is stone and slippery and steep in parts, so wear appropriate footwear - at least trainers and socks. We hiked in Birkenstocks and regretted it. Others hiked in flip flops - never do this. This means it is still possible to hike in Birkenstocks. As is typical for southern France beaches, the beach is rocky but the water is clear. There are no facilities in the Calanques, so bring everything you think you will need.