Ahhhhh, our friends, the Juggernauts, are back. They are just as tough as before, and maybe tougher...their close range weapon shoots the same bolts as the Enforcer's gun, and they are just as deadly. However, this level provides many places that you can take a shot, then back away, so these shouldn't be much trouble. Make sure you use any rechargers and save terminals frequently. Also, you may want to consider using the fusion pistol as well as the rocket launcher for these guys, as its effect is the same as it is on Troopers and Hunters.
At one point, you'll need to swim across the lava to reach an opening. (This is in the lava room that has the save terminal and the smaller room.) This isn't a very long swim, and you may be able to save some damage by using grenade hopping. In any case, beyond the opening you'll find the switch that will open the door that was initially blocked to you. Swim back across, then recharge and save before continually.
One room contains 4 destructible circuits. Two of them (the one you first see when you enter and the one closest to the other door) will open the door, a third will cause the lava levels to rise, and the fourth will cause the save and regeneration terminal at the start of the level to become inoperative. Needless to say, you only want to destroy 3 of these switches. Hit the 2 door ones first, then, as far out the door as you can, hit the lava switch, then run back to the start of the level. You'll notice that you can now explore the other side of the level with the lava levels readjusted as such.
There will be one lava filled room that contained two Juggernauts. (This is after you have caused the lava levels to change.) Once these are destroyed, and you have saved up, you'll need to swim across the pool, sticking to the right wall, to reach another ledge. This will take about 1 level of shields. Fortunately, there will be a 2x recharger at this ledge, so don't worry too much about staying too long in the lava. After this ledge, you'll pass through a small hallway into a room with a square inset into the floor. This will teleport you into the final room of the game. Arrange yourself so that you are facing about 125 degrees counterclockwise from the direction that you entered the room, and make sure your swim key is ready to go. Oh, and make sure you switch to the rocket launcher.
Once you teleport into the final room, you'll be under lava. Swim up and out (the direction I've indicated above seems to get you out the fastest). With rocket launcher at hand, ignore the baddies in the center, and just run like heck around the outside of the room, dodging the lava pools and the occasional alien as you run. You'll want to run with the wall to the left, as to give you maximum visibility of the aliens on the right (considering that you have a rocket launcher on your shoulder). After a few laps, the aliens should be fighting themselves. Continue running, watching your radar until you see that only one or two aliens are left. This will most likely be a large blue Hunter, and a Juggernaut. Hopefully, the Hunter will be aiming at you, while the Juggernaut is going for the Hunter. Keep running, and if you think you can get a shot off with the rocket launcher at the two, do so. At some point the Hunter will die, and then you have two choice to continue...
1) Continue pelting rockets at the Juggernaut from a distance. You'll have to be quick to get the aim, and then to continue running. It would be even more helpful if you can run in one direction and shoot in another (with the look modifier key) but this can be difficult while avoiding the lava pools. Switch to the plasma pistol if you run out of rockets. Eventually, the Juggernaut will fall, at which point you should try to get into the farthest corner that you can in order to reduce the amount of damage that the explosion does.
2) Rush the Juggernaut with a plasma pistol. If you stick as close as possible to the alien, he won't be able to direct his fire that far in, and you should be able to continually hit him. Again, once he falls, you need to get out of there as fast as possible to avoid taking too much damage.
Either way, you need to avoid taking ANY damage from any source in this last room. Even at a far distance, the explosion of the dying Juggernaut will take nearly 1.5 shields, which is just about what you will have left after getting out of the lava. That is why the swim across the lava to the 2x regenerator and the teleporting room is very important...if you time everything correctly, you can have *just* above 2x shields, and you will not have to use the regenerator.
In order to read the final terminal, hit either switch to bring up a platform in the lava pool in front of the terminal, and read away. See you in Marathon 3 :-)
In the lava-filled room that has the save term and the 'safe room' that is enclosed, there is a door that you can't open in the back of the safe room. This door opens from the 4th switch that you destroy (see above) that causes the save term and shield regenerator at the beginning of the level to fail. You also need to hit the infamous switch that is under the lava, against the side of the wall near the safe room. Once you hit these switches and return to the safe room, enter the next room, but watch for Hunters. Once the aliens are dispatched, continue on, dropping into the lava (not swimming), moving as far forward (swimming), then getting out of the lava into another narrow corridor. At then end of this corridor is a shield regenerator and a switch which creates a window on one side of the room. There is also a small inset square on the floor...stepping on this teleports you to the Bungie credit room, but your work isn't done yet...you need to immediately move off the octagon that you are one to avoid being teleported out of the room. Once you have teleported and set in the credit room, pull out the WSTE-M's and blow the aliens away. There is the credit term and 3x recharger in the opposite corner of the room. To exit the room, return to your starting point...stepping on this will take you to the final room... but if you followed the instructions as listed above, this room will be filled with lava, and you will have little chance of surviving here. You can empty the lava the same way (by hitting the appropriate switch in the aforementioned room), but then you will have to run through the lava to get to the credit room. Thus, the credit room should be explored once, but not used in the successful completion of the game.