The tourist information gives a leaflet with a map and a walking tours in the area of the harbour of Lorient.
I chose to start with Port-Louis, a peculiar little fortified town with a citadel. The tour along the rempart mixes history and landscapes, which are very various as we can see Lorient (the harbour, the bunkers...), Larmor-Plage, Gâvres, the Island of Groix, further away in the Ocean Atlantique, and even Quiberon if the weather is good. It lasts around 1h/1h30.
The town wasn't full of tourists as I expected it to be, with the Festival Interceltique in Lorient just near it. Even if it is supposed to be peak season, it was calm and I enjoyed it even more.