1. Follow Alyx off the elevator to begin Half Life 2: Episode One's lengthiest level, Urban Flight.

2. Find this locked gate. Note the orange socket to the right.

3. Backtrack past the elevator to this gate. Turn the crank to access the supplies inside.

4. Buried beneath the boxes in the far/right corner is the hand crank Alyx is hoping to find.

5. Return the crank to the socket and open the gate.

6. Ascend the stairs to finally reach the surface. Listen to Dr. Kleiner on the big screen.

7. Pull the metal sheeting away from this barricade.

8. A supply crate - and surveillance drones - are on the other side.

9. Clear another barricade then battle these troops, apparently alerted to your presence by the drones. Be sure to grab an SMG from the troops.

10. Slip passed this citadel barrier once it moves out of place.

11. Three antlion pits are accompanied by, once again, three cars.

12. Plug the antlion pits with the cars (or just run passed them) then follow the road ahead/left to this door. Pull the planks off to enter the building.

13. Combine are setting up mines. Toss chairs into the laser beams to trigger the mines and dispatch the soldiers.

14. An inferno ensues, fueled by a propane tank in the room to the left.

15. Position one of the milk crates so that it supports these pipes. You can then cross the pipes to the ledge and turn off the gas.

16. Collect the area's supplies then ascend these stairs.

17. More mines are on the second floor. Watch this zombie trip them and blow himself to smithereens.

18. More zombies are in the next room. Don't destroy the roller mines you'll find; they'll take out the zombies and will make your advance easier in the upcoming area.

19. Grab supplies from the floor then take a peek out the window -- a sniper has taken up position at the end of the road.

20. Descend these stairs and encounter another zombie and more roller mines. Take the roller mines to Alyx for reprogramming -- they'll be excellent escorts.

21. Duck outside then sprint behind the building on the right where you'll find a pair of supply crates.

22. Crouch then seek cover behind this red car. Stand, sprint, then crouch again behind the blue car to advance farther down the road. Note the suit energy in front of the blue car.

23. Antlions! If you have your roller mine escorts with you they'll clean up your ant problem nicely.

24. Once you are in front of the blue car the sniper won't be able to target you. Toss one of your reprogrammed roller mines into his nest to flush him out - dead. Alternately, use a grenade found in the supply crates ahead to blast him out.

25. Alyx will take up position in the sniper's nest and shoot this ladder free. Climb the ladder to advance farther down the street.

26. Zobmies attack, but they're no match for Alyx's sniping skills. Enter the building through the door on the right.

27. A supply crate - and a toxic head crab - are here on the right.

28. Head upstairs then remove the planks covering these windows on the left. Alyx then has a clear shot at the line of zombies marching your way.

29. Descend the stairs at the other end of the hall then find this supply crate before returning to the street through the door on the right.

30. Remove this metal sheeting so Alyx can snipe the gunman on the other side.

31. Push the white car into this antlion burrow.

32. Slip behind this barricade once it opens up. Soldiers keep spawning until you do.

33. Bust open the supply crates while Alyx catches up. Advance into the building after she deactivates the force field.

34. More trouble -- it looks like the core is going critical again.

35. Bust open these crates once inside.

36. Head left to this battle with several combine troops -- they'll drop the highly-coveted pulse rifle.

37. Find plenty of supplies here on the left.

38. More soldiers soon attack from the door to the right, where you'll find health and suit energy stations. Both exits here lead to the same hallway.

39. Fight passed anther soldier then ascend the stairs to your next auto-save checkpoint and more supplies.

40. Toss any unused supplies to the pavement below before dropping through.

41. Combine troops are battling an antlion bull outside. It's tempting to hang back until the bull finishes them off, but I found it best to begin work immediately -- just keep out of everyone's way.

42. Your first task is to plug up the two antlion pits.

43. Here's the second pit. Now at least you won't be bothered by additional antlion spawns. The troops should be history by now.

44. As befits the name, "bull," this large antlion attacks by charging head-on. Keep moving to avoid his charges and get in as many shots as you can.

45. The machine gun emplacement seen on the right can be a good place to circle around. Unfortunately the bull is too fast to make the machine gun itself much use.

46. Before long he'll succumb to your fire, and Alyx will take up position at the machine gun. Rush through the opening in the barricade and find a health station to the right.

47. Enter the building through this hole to the left.

48. The door on the right is locked. Blow up the barrels in this corner then deactivate the mine before crawling into the vent on the left.

49. Keep right at the first junction then climb this ladder.