Molloy, 10 km to the west of Port-aux-Francais along the north shore of the Gulf of Morbihan, is the site of a former observatory, established on 7 September 1874, by an American expedition led by G. P. Ryan, to observe the 1874 Transit of Venus.

The eastern portion of the peninsula is relatively flat, with the surface composed mainly of alluvial deposits of glacial origin, and altitudes not exceeding 200 m. However, the western part is hillier and reaches 900 m at Mont Crozier near the isthmus.

The easternmost point of the peninsula, and of Grande Terre, is Cape Ratmanoff, north of which is coastal Lake Marly.

[4] The Courbet Peninsula holds the largest breeding population of southern elephant seals in the archipelago, with 43,782 females recorded in 1997.

[4] Much of the peninsula has been identified by BirdLife International as a 600 km2 Important Bird Area (IBA) because of its value as a breeding site, especially for seabirds, with at least twenty-two species nesting there.