Half-Life/Surface Tension

So we've finally reached the surface. Surface Tension is one of the largest levels in the game, both in length and sheer size. Outdoor environments have properties that allow a number of unique situations and enemies that you have not yet faced. Because some of these situations involve combat in large, complex areas, there's no one specific way to play these levels. You'll have to use your experience and creativity to analyze the particular situation that you are and play it accordingly.

The Dam
Walk through the garage door before it closes, but be wary. There is a marine to your left and one to your right, as well as several more a little farther waiting to ambush you. Using the magnum or shotgun, take out the ones right outside the entrance. Shooting the explosive barrels may take out a few of the ones farther up the canyon and save you some health and ammo. Grab the ammunition the grunts dropped and proceed with caution. Stop near the end of the tunnel where you are still somewhat protected and survey the next area from relative safety.

Here's the situation: up ahead, the road goes over a dam and ends at a closed blast door and an artillery gun emplacement. If you try to run straight across the dam, artillery fire will blow you to pieces. There is an Apache helicopter circling above that can't see you for now, but will fire at you once you are out in the open. The left side of the dam is dry, but is an unsurvivable drop. The right side, on the other hand, is full of water, but contains an Ichthyosaur (I hope you have some crossbow bolts). Every once in a while, the Apache will fire on the Ichthyosaur damaging it a little more. Technically, if you wait long enough, the Apache will kill the Ichthyosaur, but whether or not you wait for this is up to you and the supplies you have. There is a tower on the right side in the lake that has a protective alcove with a health station and a control that controls the turbine. You will need to hit this button to turn off the turbines. When you have done that, you'll have to jump into the lake and kill the Ichthyosaur. Once the Ichthyosaur is gone, swim back down to the bottom of the lake and find the valve wheel. Turning this opens the grates covering the pipes through the turbines. As long as the turbines are off, you will be able to swim through to the river on the other side of the dam. Grab the battery on the rocks and duck down underwater when the Apache is about to fire at you. Follow the river down the canyon and climb the ladder onto the structure at the end. Crawl into either pipe to escape the Apache.

In the Sand
Whether or not you killed the Apache helicopter at the dam, there will be another one circling overhead here. The pipe terminates in a deep canyon, giving you two choices. The left path goes to a cave with a few headcrabs, a dead marine, and some supplies. The path to the right leads to several crates of ammo and a ladder in the concrete wall. Climb the ladder and jump across to a small area with some batteries, ammunition, and high walls for protection. This is the best place to take out the Apache. Get out your Tau Cannon and charge up the secondary fire mode when you hear the Apache approaching. As soon as you see it, hit it in either the cockpit or at the base of the rotors. Take shelter behind the tall concrete walls when it shoots at you and repeat this as many times as it takes to bring it down.

With the Apache gone, this part of the level is a whole lot easier. When there is no more danger, jump back to the ledge and follow it around to find another ladder. At the top of this ladder is a rather large military fortification in the sand. Follow the rock wall to the left and take the first passage you come to. This leads to a small sandy area guarded by a large green tentacle. If you need the supplies within the tentacle's reach, crouch to avoid making sound and throw a grenade for distraction if you have to. If you shoot this tentacle a couple of times, it will retract for a short while, allowing you to get the stuff scattered near the tentacle's base.

Go back out the way you came and follow the ledge to find another tunnel in the wall. This leads to an opening containing three grunts. There is a large boulder on the right side of the clearing and a tower on the far side. The crossbow or magnum are good for this long range battle. When the marines are gone, head into the tower and turn the wheel marked "Storm Drain Hatch". There is also a small alcove in this area with supplies, but it is booby-trapped with a laser mine. The other alcove in this area leads to another opening filled not with marines, but with landmines.

Save constantly from here to the drain opening. The landmines are mostly out in the open area, so stay to the right side as you make your way through this area. Crawl under the fallen rock, making sure to stay as close to the rocky wall as possible. There is a mine in the sand right in front of the barbed wire, so jump over it or shoot the area until you hit it. Once you've made it to the slightly darker colored sand slope on the far side of the barbed wire, you're safe, as there are no mines on this slope. Jump over the barbed wire and climb down the ladder into the storm drain. At the bottom of the ladder, smash the grate and crawl through the tunnel.