The Quinconces Square (known locally as the Esplanade de Quinconces) certainly impresses with its size - at 12 hectares (30 acres) it's one of Europe's largest squares. And it's impressively situated on the banks of the Garonne, laid out in a semi-circle with trees planted in geometric patterns based on the number five (it's these patterns that give the Esplanade its name).
Laid out in the early 1800s, the square is adorned by some massive public statuary. There are rostral columns, statues of Montaigne and Montesquieu, and an immense monument to the Girondists, who were executed during the Revolution.
The monument is a riot of bronze horses and warriors. During WWII it was dismantled by the Germans and the bronze melted, but it has since been restored.
Practically all the public transport of the city runs through this point, so you'll find it easy to get to.