Collect the indicated number of artifacts to unlock the corresponding concept art.

Allies: 12 Artifacts.
Co-op Levels(Wii Only): 8 Artifacts.
Cutting Room Floor: 36 Artifacts.
Enemies: 22 Artifacts.
Extras: 20 Artifacts.
Istanbul: 28 Artifacts.
Nepal: 26 Artifacts.
Odin And Seabed: 32 Artifacts.
Panama: 18 Artifacts.
San Francisco: 14 Artifacts.
Sudan: 2 Artifacts.