Walkthroughs
These tips are just general objectives, they don't take you everywhere you might want to go. Beware these are major spoilers!!! Only read them if you are severely stuck.
Level 1:
1.Go into the theatre via the back door.
2.Get a key in the projection booth.
3.Get the shotgun in back of the counter with the cash register.
4.Go to the arcade.

Level 2:
1.Go into the bookstore.
2.Go through the door that opens with the right button combination. If you're having trouble opening the door, keep trying different button combos. Go up the elevator and get the key.
3.Go into the little room outside, to the left of the bar. Destroy the building.
4.Go to the building ruins, and get the key.
5.Enter the building. Go past the pool table, and take the first right.
6.The key is hidden in a cabinet under the bar.
7.Go to the strip club. On the right wall when you enter is a vent.
8.Open the curtain and jump onto the cylindrical platform. Jump from there to the ledge that used to be behind the curtain.

Level 3:
1.Get out of that chair!!
2.Explore the area until you reach a hall in which a wall explodes. Enter the new hole and get the key.
3.Go back into the hallway, and turn right, continuing down the hall.
4.Duck below the tripwire, and go up the ramp. Enter the room at the top of the ramp that has tripwires on the doorway by jumping over the tripwire.
5.Get the key. Turn around, and make sure you kill the pigcop before he trips the wires.
6.Go back down the ramp, and turn right into the big room. Go down the ramp and into the key door.
7.Kill all four turrets and the two RPV's, and get the key. Return inside to the big room.
8.Open either red key door, and go to the room with the hologram in the middle.
9.Hit the switch that rotates the walls, and switch the Cell Blocks' shields off. Rotate the wall, and go back to big room.
10.Go out the big room the way you came, and back up the ramp.
11.In one of the cells, there is a poster covering up a hole. Go into the hole.
12.Go into the submarine.

Level 4:
1.Get out of the submarine (use the red buttons to open the emergency door).
2.Search the cliffs for the blue key.
3.Go into the factory. Travel on the production line to get the red key.
4.Use the red key to access the shrink ray. Go into the small tunnels to open the door lock.
5.Go back to where the first shrink ray is and enter the unlocked door.
6.Search underwater for a switch that raises the water level, and swim up to the surface (you should be in a new area).
7.Search the new cliffs for a little control room. Hit the switch that opens an underwater door.
8.Go back underwater and find where the door is that you opened. Go into the underwater room and hit the switch that opens another door.
9.Enter the door. To get through the gears, you have to go in between them. both of the gears have a tooth missing; you have to run through the gears right as the missing teeth comes around.
10.Swim to the surface. Follow the current until you reach the big open area. (I suggest you get out of the water and on to land as soon as possible.)
11.Go up to the little control room and hit the switch. You will see a wall open out the window.
12.Go up the slope with the water running down it, and turn left. Hit the switch, then cross the slope and jump to the ledge.
13.Step on to the moving platform (the one you saw when you hit the switch in #12) and shoot the switch. Quickly jump on to the other moving platform (this part can be tricky, don't get discouraged!).
14.The rest is pretty straightforward.

Level 5:
1.Exit the sewer tunnel and go down the ramp into the slime (call this area #1).
2.After the first big waterfall, jump onto dry land. Search the area for the blue key.
3.Go back up to area #1. If you face the sewer tunnel from in the slime, to the left of the structure is the blue key hole.
4.Go through the blue key access area, and once you come out of the short cave, turn to the left.
5.Jump over and enter the cave. Turn right in the cave.
6.When you come out of the cave, jump to another cliff.
7.There should be a sign that says "The San Andreas Fault". Go up to the sign, and an earthquake will occur.
8.Facing the sign, turn 90 deg to the left, and jump down to the slope with the healing. Keep on jumping down until you reach the bottom.
9.Enter the cave and go up the stairs. When you get to the well-lit area, turn left and go up more stairs. 10.At the top of the stairs, fall into the room below you. Turn right and hit the "hand" switch. 11.Go through the hall and drop off another ledge. 12.Hit the hand switch to make a stair case. Go up the stairs. 13.Look out of the cross-shaped hole. An earthquake should occur, and a new cavern will become accessible (you'll see it through the window). 13.Hit the hand at the top of the stairs, and jump onto the rising platform. (You may have to do this a few times.) 14.Hit the hand switch at the top of the platform to activate the shrink ray. 15.Shrink and go through the small hole. 16.Enter the cavern that became accessible when you caused the earthquake, and enter the alien ship!