The achievements are all obtainable in one play through. More easy guides here to get 100% here

Controls

W = forward
A = Left
D = Right
S = Back
F = Torch
H = first Aid Kit
E = interact
Left mouse button fire
1 = Club 2 pistol 3 shot gun etc depends which weapons you have picked up
space bar = jump
Shift = run

1) Press F to enable torch then pick up your weapon at the start after the ceiling collapses on the giant creature image below then exit through the blue door (if doors not unlocked just wait) image below




















2) Turn off your torch the enemy will see it. Jump down and see a couple of cockroaches press 1 to equip your club and batter them. Follow the path forward encounter 2 more cockroaches. At the top right of the screen are 3 boxes open them to collect ammo. Then go to the gate (image below) and press E to pull the lever.




















3) Carry on further and you'll see two turrets in front of you. The hint says "Shoot at the glowing element" but I would advise you to run along the edge of the wall (to your right) and lean against the corner (circled in blue) and then shoot them (see picture below)




















4) In the next room you will see a arch on the left and the right ignore the left side and go to the right you need to quickly close the cockroach holes by blowing them up with dynamite.




















5) Carry on and kill the worm the turrets are optional you'll see a blue door and a crate take the shotgun from the crate then go through the door and shoot three waves of enemies (there is a "fountain of youth" to your right 2nd image below)







































6) When you have cleared all the waves of enemies the game says: "Kill all the enemies" for this you need to collect 4 keys open the doors and kill the enemies behind them. First, run through all four passages and collect the three keys (watch out for traps). Key locations below.

























































7) Once you have collected the three keys, you need to open the doors in the CORRECT ORDER, as one of them holds 4th key. Stand in front of the stairs there are two doors on the right and two doors on the left. The key behind door No. 3 is on the right (see images below). In the last image is the way out there just run forward all the way.











































































8) Kill any crawling creatures and turrets that can teleport




















9) Turrets again. Quickly kill the top one with a pistol and aim for the glowing red on the other two.




















10) Grab your rifle and kill everything (this is the last new weapon in the game). Then you need to break the portals by shooting at the blue balls. Once in the next room shoot the blue light (image 2 below)







































11) There is no hints from the game from now on only tasks but we need to explore all the outer rooms again for living aliens. We go everywhere we can and kill everyone. The most important thing is to kill those who are hiding behind a shelter (see image 3 below tip - when you get back to the stairs and three doors go straight look for the skeleton image 2 below). Beware of traps.

























































12) Time to go to the exit.




















13) We go further on and find a funny bug but in one of the boxes there is a pistol that we picked up at the very beginning of the game.







































14) In the next room you have to fight with mini-boss by the way it is much more difficult than the main boss. To kill him (mini boss) you need to shoot him in the head then wait for the shield to fall run around him and shoot him in the head with a shotgun.





















15) The penultimate level. In front of you are 4 buttons and 4 rooms open them. The rooms also have buttons and dynamite presses and collects checkers. I advise you to go through them in the order, in the images below. 1) Kill enemies and Jaeger.


























































16) Room 2 you need to jump and run quickly to get minimum damage. We also jump over the floor saws.







































17) Room 3 enter press the button and go along the middle beam in the middle of the screen (along the line between the squares see image 2).







































18) The fourth room. We stand on the platform and go down (we need the dynamite). Blow up the burrows and climb to the top. Press the last button and run to the portal (see images below).

























































19) The last level. Go forward kill everything you see.




















20) Enter the boss room and see a giant squid. Let's do this the easy way. Enter the room but do not go in too far. Shoot the two central tentacles from afar then move to the edge and shoot the outermost ones. Game Completed.