Hotel de La Plage Mahogany has a supreme location. It is located just on the opposite of the Plage du Bestouan overlooking a breathtaking view. I would seriously suggest their rooms with the sea view though. The interior of the rooms are not that fancy but the large balcony outside gives you perhaps the best view Cassis has to offer. Be it watching the sun-set or just lying on the sun beds having a piece of mind, it offers perfect relaxation. If you wonder a walk to the calanques or to the downtown (marina) Cassis it is still at easy walking distance.
Remember this is not a luxury resort with all in one facilities, but it is a good value for what it offers. Simple yet clean accommodation, decent breakfast (usually charged optionally) and excellent location with a real piece of mind.