- This level occupies the map slot MAP10. For other maps which occupy this slot, see Category:MAP10.
Map10: The Radioactive Zone is the penultimate map for Harmony.
- The action is quiet at the beginning. Go down the steps, attack or evade the sniping enemies, and proceed to the northwest.
- You should come across a building. Press the switch to open it up, but kill the predator guarding it.
- Next is a nukage run. To start it, enter, and run across the north-west part of the pit. The floor will slowly rise. If you start to run low on health, use the medikits scattered on the ground. When the nukage reaches the top, run to the side where there is no nukage. (If playing co-op, it's best if one player enters. The others get a shortcut to the right.
- On the southwest corner of the tower, flip the switch to reveal green armor. It also opens the exit jump on the southeast corner.
- After jumping out the tower, take the next nukage run, following the east branch. (The south branch returns you to the start, which is bad.)
- You need a green key, and there is only a roundabout way of reaching it. First, head to the building to the north, enter and climb the stairs. Follow the ground arrow and make a window jump to the ledge. From the ledge, enter the south building.
- Flip the switch in the building, and you may head east to a courtyard, where you can find a chaingun. Proceed north, dealing with the enemies as necessary.
- Within the northeast building, head left and turn north. While you can enter the side room to collect ammo, return to the main corridor to continue (because dropping down the well makes it harder to safely attack the Phage.)
- Head west, Flip the switch to reveal the north path. Run down the corridor as the crushing ceiling will activate.
- Turn left, and you will enter a maze. It may be easier to wall-run rather than being in the maze proper. To complete the maze, you need to approach the south-west corner. As you make the approach, the walls will lower, and you will be attacked from two directions at once. (If wall running, try crossing the trigger line from the south, and using the first half of the maze for cover.)
- Continue south, and you will reach the key. Backtrack to the previous building and use the key to open the door leading outside.
- Run across the nukage and turn south. Once you enter the cavern, you can take the lift to the surface.
- After the lift, head south and flip the switch to reveal the key, armor, and a path back to the green key gate.
- Head south and enter the building. Use rockets to clear out the predators.
There are no secrets on the map.
Although this is not counted as a secret, you can use the grenade launcher to rocket jump to the exit, because Harmony permits free-look. From the start of the map, head directly east, and there is a predator on a brown rock. Kill it, and aim the grenade launcher downward. Run forward and fire, and you will be propelled upward.