Morbihan offers a huge number of Neolithic megalithic remains. You can start with Menec alignments where the Maison des Megalithes is found. There you can get information about where the most important or interesting sites are, along with a plan. Carnac houses the museum of prehistory and it's the most iconic landmark in the area. In Locmariaque you can see the great menhir and dolmen merchants table, plus a large burial mound. Don't worry about time as you can visit all of this with a day without fear of missing anything.