Half-Life/Forget About Freeman

By now, the military has discovered that they're fighting a losing battle. They have ordered a full retreat and are now performing air strikes as a last option. In the following levels, although they will not disappear entirely, you will see less military personnel and more aliens, though the battle between continues.

Back Underground
At the top of the small set of stairs, save the game, and be careful. As you enter this room jump through the hole in the railing on your left as a chunk of the ceiling falls where you just were. The ceiling continues to fall in chunks, squishing everything under it. After the third chunk drops, jump up onto the shorter of the chunks and make your way over the fallen ceiling pieces to the door at the end of the room. Crouch and crawl through to find yourself in a run-down security station.

There is a radio spouting messages and a level that controls a ceiling-mounted turret. A security guard is just outside the room hiding behind a large box. Jump out the window and enlist the guard for help. As you walk into the large part of this room, several alien grunts and vortigaunts warp in. Take them out quickly with the help of the security guard, then walk down the ramp.

To your left is an brown alien web blocking the path. Snarks and other aliens are hiding back there as well as some supplies, but it's really not worth it. Instead, go right and kill the vortigaunts that pop up in the hallway using the explosive boxes if you want. To the right is another glowing alien sphere that will erupt when you get close, sending a pack of snarks your way. Fire the hivehand at them as you retreat or run away until they explode, then head back and turn the valve wheel to open the hatch and climb on down.

At the bottom, there is a small room with a headcrab. Shoot it before it jumps through the lasers and activates the tripod mounted chaingun. Destroy the chaingun and go down the short tunnel. There are two canals here as well as several wandering headcrabs. Break the boxes for first aid kits, then crouch jump over the grating guarding one of the canals into the water on the other side.