This level occupies the map slot MAP05. For other maps which occupy this slot, see Category:MAP05.
MassMouth is driving the hover truck inside the icy tunnel. Suddenly, a block of ice falls of the ceiling, and the truck slams into it, knocking MassMouth out. He awakes a few moments later.
Jump off the truck's wreckage. You will see a door, which leads to one of the tunnel's maintenance areas. Before going there, check out the truck remains. You will find some railgun clips and stimpacks, but you will encounter a Genestealer Majora. Also, another part of the vehicle was flipped on its side, you can go there if you want. Do you remember that Yodan who was frozen in the back of the truck? Well, the block of ice that imprisoned it shattered in the impact, so the monster is now conscious again. Kill it with high precaution, and do not forget to pick up the two boxes of shell and the megaarmor behind the little dark wall. Now go to the maintenance area. You can look for some ammo and health on (and behind) the pipes at the entryway. Go through the hall and take care of the Genestealer Minora. There is a small door, but do not open it yet. Note the presence of a hole in the ground. It is the entry of a ventilation shaft.
Explore the hall and you will come to another pipe. Upon approaching it, it explodes (killing a Minora in the process) and make blocks of ice fall on the ground. Go back to that small door and open it. Kill the two Ontras in the room (pick up the shells and the stimpack) and flip the switch. The air shaft is now open. Walk through it and you will come out in some sort of docking bay with three stationary hover trucks and a control terminal. Go to the terminal, slay all the Ontras and pick up the items. There are three switches which have no purpose, and a fourth switch that opens a nearby door to a train system. Go there, shoot some Genestealers and enter the train by jumping into a hole on its roof. Look for a switch once you are inside, and the train begins to accelerate. The bad guy from the first level talks to you by radio transmission, and a poisonous bomb explodes in the train. A green cloud forms and puts MassMouth to sleep.
Our hero wakes up unarmed in a cell guarded by an Ontra. The bad guy comes in and the player finally gets to see his face. The main villain is actually John Romero. After taunting the extra-terrestrial once more, Romero exits the cell, and the game goes back to first-person view mode. Do not touch the forcefield that keeps you in your cell and let the friendly Trooper hack it. It will vanish a few seconds later. Quickly grab your weapons and take down the Ontra. It will drop a yellow keycard upon dying. Pick it up, exit your cell and open the door on your right. The Trooper warns you about a bomb in the complex set to go off in a minute and reveals that according to his scanners, Romero's ship is headed for Zeeble, MassMouth's homeworld. There is no time to lose. Open the next door and kill several more Ontras. You will see the bomb and a combination with three figures. If you let the Trooper try to hack the code (which changes everytime you start a new game), you will not have a lot of time to enter the code, so you should randomly mash the buttons until you defuse the bomb.
Finally, open the door leading to a ship. Kill the last Ontras, get aboard the vessel and the next level begins.
There, a text screen informs you that Romero may want to add The Worm to his "giant bug collection".
There are no secrets in this level.