The classic views of La Rochelle all include the towers that guard the entrance to the old harbour, so I am not about change that approach.
In the first one you can see that the old city walls join onto the tower, there is a walkway along the top of the walls from the towers for some distance - and at the end is quite a nice beach.
La Rochelle combines history with the seaside, there are substantial marina berths, a large aquarium while there is a modern side with commercial docks and the factory where the TGV trains are built.
There are plenty of restaurants along the side of the oldest part of port, you can spend a pleasant hour walking along comparing the menus.
The old port area includes many separate basins used as marinas, one also has the floating exhibits of the Maritime Museum including the survey ship seen here.
Another view of the Tour St. Nicholas, proudly flying the French flag, you can see the the Cathedral in the background. It is in the old part of the town with a maze of streets to explore. The right hand photo is of the emblem of La Rochelle carved on one of the towers.