We visited the Calanques National Park by kayak from Cassis and by foot from Luminy (we got there by bus from Marseille - B1 or 21). Both ways were great.
The kayak trip was for 12 peaople and I have booked it in advance - I describe it in the review of the organizer.
On a walking trip we went alone with a map from the tourist office. Start was in Luminy first to Calanque de Sugiton, then along the coast to Calanque de Marigiou (on the trail was a ladder, rope and steep :)), then to Baumettes and by bus to Marseille. The trail was sometimes difficult but we managed. Hot but worth it. Wonderful views !!!