You will see the Crêperie de St-Germain, a green stall on the corner. Looking next to it, you will see the metro station exit Saint Germain de Prés (exit 1 - Church side). If you are coming by taxi the best address to give is Place Saint Germain des Pres, then walk round the corner to the Boulevard.
We end in the Latin Quarter, just down the road from the Notre Dame cathedral. You will be perfectly placed to visit the cathedral after if you so wish.