You can't do much else but proceed forward until you slide down. [100 XP]. Look to your left to find some [SALVAGE], and like also [SHOTGUN PARTS 1/3]. There are also some [ARROWS] in this area. Proceed through the hole on the right and wade through until you reach the end.
When you get out, hide behind the crate and kill the guy on top of the building with a headshot. Wait for the guards to finish their conversation, then kill one of them with a headshot. Don't get the contents of the [SALVAGE BAG] before killing all nearby enemies first; it's a trap. There's a red explosive barrel near the stairs that you can shoot when enemies are nearby, although it's not necessary to do this. Search the place to find some [ARROWS] on the walkway, and some [RIFLE AMMO] near the other building, then go upstairs to find some [SALVAGE].
Follow the linear path and collect [SHOTGUN SHELLS] along the way. Move over the beam to cross the gap, kill two enemies and move around the corner to finish a third one. You can also find [RIFLE AMMO] near this corner. When you reach the chopper, pull away the back with a rope arrow and move inside. After the scene you'll have access to fire arrows. [100 XP].
You can put these to good use right away by killing a few enemies down below. Wait until some enemies start hiding in the building to the right then shoot the red explosive barrel near the fence to waste some of them. This fight can get fairly hectic, especially because enemies will soon come from the side as well. While Lara's fire arrows can destroy some of the fences in the building across the street, you'll soon want to switch to your rifle and make good use of the explosive barrels on the right/west side of the area. After killing all enemies you can start exploring shanty town, which houses many, many collectibles, items and ammunition.
You'll find the 'Helicopter Hill' base camp close to your starting position, on the far northwest side of the area. The map is going to be very useful while exploring shantytown, so be sure to consult it every now and then. It's likely that you can upgrade your rifel into the [ASSAULT RIFLE] at this point. If not, finding some more salvage will surely solve that problem soon enough.
• If you haven't collected these yet during the heat of the shootout, grab some [ARROWS x2] and [RIFLE AMMO] from the walkway you started out on. Also loot the numerous bodies you left behind.
• You can find some [ARROWS] on the stairs leading down, close to the camp.
• Head down and stand in the center of the square. Face the chopper to the north and you'll notice a burnable piece of cloth directly in front of you; shoot a burning arrow into it, then pull the thing down with a rope arrow to destroy the first of five effigies, part of another challenge. This guide will refer to them as: [LAID TO REST - #1 EFFIGIES], this of course being number 1.
• From the ground floor, move to the east. Ignore the barricade for now and search the shack near the fence to find some [RIFLE AMMO].
• You can find [SHOTGUN SHELLS] near the destroyable barricade to the east.
• North of here, in the corner of the area, you can find a [PLANT].
• It's possible to move underneath the house south of the square. Here you'll find [SALVAGE], [RIFLE AMMO] and [SHOTGUN SHELLS]. You might at this point receive [SHOTGUN PARTS 2/3] as well.
• [RELIC - #1 INRO (DECORATIVE INRO)] can be found on the ground floor of this building (which stands immediately south of the camp square.
• Still on the same floor, one can find [SHOTGUN SHELLS] on the other side of the building, near a barricade.
• Climb this building to its top to find an [XP BOX], [RIFLE AMMO] and [ARROWS].
• Moving to the west of the center building, you can find a [SALVAGE BAG] on the 'first floor' walkway. Run around the corner to find [RIFLE AMMO], [ARROWS], and a [GPS CACHE] a few steps further around this corner.
• Climb this building to the next floor to find some [SALVAGE]. Climb to the top to locate a rope attachment pole (shoot it into the small beam sticking out of the roof directly in front of you, of the center building). You can also find [SHOTGUN SHELLS] here, as well as the first [SILENCER - #1 ALARM]. Destroy four of those to beat that challenge.
• North of here, (after jumping back to the ground floor) underneath the stairs is a small room that contains [SALVAGE] and [RIFLE AMMO].
• From the first floor of the center building (south of the northern camp square) head south and destroy the barricade, then move into the southern building (destroying another barricade to enter). Inside you'll spot some blood stains on the floor. Look around to find some [ARROWS], [SALVAGE], and [DOCUMENT - #5 ENDURANCE CREW (GRIM: THE GOOD OLD DAYS)] on the table.
• Climb to the upper walkway to find some [SALVAGE], [SHOTGUN SHELLS], and [DOCUMENT - #4 CONFESSIONS OF A SOLARII (TOIL AND DISTRACTION)] on a crate. You'll likely also collect [RIFLE PARTS 1/3] at this point.
• From the ground floor of this building (south of the center building that was in turn south of the camp square), proceed outside (slightly south) and turn right/west to blast another barricade. The shack behind it contains a [GPS CACHE], and you can destroy another barricade to clear another path to a square with a trap in the middle and some explosive barrels standing around this.
• At this southern square, with a [SALVAGE BAG] trap in the middle, simply activate the trap and shoot the pulley to collect the loot; there are no enemies nearby. You can then grab the nearby [SHOTGUN SHELLS] too. Leave the explosive barrels standing for now. Their function will become apparent soon.
• Approach the doorway to the south to discover an optional tomb entrance. Don't just recklessly enter, but jump over the trap in the door way to collect [SALVAGE], [ARROWS], [SHOTGUN SHELLS] and a [LARGE SALVAGE BOX] inside this sacrificial room. You can trigger the trap if you wish; this spawns a lot of enemies. You'll first want to kill the ones quickly approaching by shooting them (and explosive barrels in the distance). After this, quickly shoot the pulley to the lower left of Lara and hide behind the wall. From here, grab your assault rifle and take out the remaining enemies, switching only to your shotgun when enemies manage to enter the room.