1. Protect Natalya: easy, medium, hard 
2. Disable Goldeneye satellite: easy, medium, hard 
3. Destroy armored mainframes: easy, medium, hard 

You start off in an elevator with Natalya, and in the easy mission, you simply stroll out and shoot everyone in the cave. But it changes in the medium and hard levels. There are three vicious guard guns placed high on the walls, and the first time in medium mode, you won't know what hit you. 

Run out of the elevator to the wall in front of you. Kill the three soldiers who run at you. The first automatic machine gun is tough, but there is a spot where you can shoot it without it seeing you. The second one is in the middle of the room, so stay covered in your first hiding place across from the elevator. The third one is the nastiest because it's high and right around the corner. Once you've taken it out, there are two soldiers just behind it and one behind you in the area where the computer controls are. Kill them. Get Natalya and she'll open a door for you. A few guards will appear in the distance. Kill them from a distance. Farther on is a room full of soldiers with big guns and grenades. Oooooh. Pick them off one by one, careful of grenades. back up if you hear that awful clinking sound. In the medium and hard levels, there are many more grenades. 

When they're all gone, instead of taking their stuff, go down the stairs to the room where you knocked of those two guys from a distance. There are weapons, and timed mines. Ahhhhhh. Now enter into that crate-filled area and pick up all of that lovely ammo. At the far side is a path, and four guards will bottleneck there for you to kill. If not, two will, and two will wait just outside to the right. 

You're in a pump room. Go up the stairs. Ascend the stairs, open the door, and back up a few steps. Soldiers will line up to get shot. There should be four, maybe five. Once that area is cleared, go down the stairs, open the door and check around the area for soldiers. Boris is in front of you at a computer console. Let him go, and make sure NOT to kill him. If you do, Natalya will quit the mission. He'll pull a gun on you, and then drop it like a goof, and then run away. Don't bother with him. Just for fun, follow Boris to a caged area upstairs that contains body armor. He'll disappear into the rocks! 

Stick mines on the two mainframes and blow them up. This should kill the two soldiers upstairs. Go upstairs and to the end of each hallway and stick mines on the mainframes. Blow them up. There are two more. 

Go back down to the main floor and head toward the only door you haven't opened. One of two giant turrets will shoot from the distance and three to four soldiers, guarding a mainframe, will run toward you. Pass in front of the door to let the soldiers know you're there, and then wait for them to come to you. After, angle yourself so that you can just see a piece of the turret on the right, but so that the gun can't actually shoot you. Take out the second one. 

Don't enter yet. In medium, on each side of the door are two more turrets aimed at you. Open the door and run straight ahead fast. You can avoid getting hit. In the easy level the staircases above the turrets didn't make any sense, but in the medium level, they do. Ascend the stairs and duck down so that you see a piece of the gun. It can't shoot you, but you can blow it up. Perform this same task for both sides. You can also shoot down the turrets from the rooms nearest them, using boxes to protect you. 

Walk out and before ascending the staircase. Go to the main part of the room with the computers in it. Take out the side computers, leaving the two center ones alone. Now, facing the big screen, ascend the spiral stairs on the right and walk to a small door in a rocky area. Walk down and get Natalya. If you're really fast, you'll have to wait for her. Lead her to the main computer area, to the central monitor. 

Natalya will start working on the computer but she'll sound the alarm. Reload your guns and position yourself in the middle of the monitor section, facing Natalya. What you're doing is getting the best possible angle on the soldiers who will come flooding down the stairs. From your spot you can hit all of them and completely miss Natalya, who's in the center. We haven't found a better way than this. Be democratic with all the soldiers. They'll flood down two to three at a time. Kill each one off, and don't let anyone get too close to Natalya. Your objective is to protect her, and if she dies, you'll have to start the mission over. A door to your right (the double door that didn't open up before), will leak a few soldiers and they'll bust through the big glass screens. This is the hardest part of the game, almost. 

When she finally overrides the computer (and it takes forever), Natalya will flee. Don't follow her. With your back to the main screen, take a right, then another right at the previously locked double doors. Make sure your guns are loaded. You'll now be way outnumbered. Enter and like before, be democratic with your lead (i.e. kill everyone). Run and gun. Pass through the first room (a locker room with a body vest in it). Take a right and another right behind a stack of crates. behind them is a small room containing the last mainframe. Reload and blow away the two guards there. Prepare for another onslaught from the door you just entered. Switch to your last mine or two, throw it on the glass encasing the mainframe, strafe to the farthest corner, and then switch back to the Duetsche. You should have completed the last mission, except escape. Be wary of each door opening and guards coming in. Head out the way you entered. Go straight out and take a right in medium and hard. For easy, take a left and head out the far exit. A double door should lead to an elevator that will take you out.