There are a couple maps that can be unlocked for Mercenaries Mode in Resident Evil 6 for the PC, PS3, and Xbox 360.
Here are the maps you can unlock for Mercenaries Mode, and how to unlock them.
Mining The Depths Map – Complete the story campaigns for Chris Redfield, Leon S. Kennedy, and Jack Mueller
Steel Beast Map – Complete two story campaigns
Check out my other article for a complete list of cheats, unlockables, tips, and tricks for Resident Evil 6.