Kuwaq Yaku – The Forge DLC
Forge of Destiny Challenge Tomb Entrance

As you approach the edge of the canyon, you'll see paths leading forward along both sides. You can choose either one since both lead to the same place. If you need arrows, take the path to the left...

...

...and grab some along the way.

After you climb the carved wall and approach the blocked gate...

...there's also a resource container sitting on the ground...

...and another container plus 2 bundles of arrows to the right of the gate

Use the resources you found to craft fire arrows if you don't already have some in your inventory. Select the bow (keyboard 1 or D-Pad Up). If you've unlocked more than one type of special arrows, press the same button again if necessary to select fire arrows.

Then without aiming, hold the Alternate Fire button (Middle Mouse/R1/RB). Lara then combines a regular arrow, cloth, and fat from inventory to make a fire arrow.

Push the jaguar-head handle to turn on a jet of flammable gas.

Stand well back and then shoot a fire arrow into the gas cloud. (Hold Aim then hold and release Alt Fire [Middle Mouse/R1/RB].)

This causes a huge explosion that destroys the blockage so you can proceed.

Beyond the gate, loot another resource canister on the left.

Then climb onto the low ramp on the right and jump to grab the elaborate wooden counterweight.

As Lara's weight pulls the mechanism down, it raises a bridge across the canyon. This only stays in place for a little while, though, so drop down and run across...

...before the bridge collapses. Loot another resource container here.

Move to the top of the ramp on the left and jump to grab another counterweight.

This raises another wooden bridge—or part of one anyway.

Drop down and before the bridge collapses, run to the end and jump into the doorway.