Beneath the Ashes is a DLC for Tomb Raider: Underworld, and is only available for the Xbox 360 gaming system. It describes what happens after the events of Tomb Raider: Underworld.
When you gain control of Lara, turn around and smash the Pot. Inside is a Treasure. Turn back around and head over to the big bridge. A Health Pack is near the left wall.
Now jump over the gap in the wooden bridge. This triggers a short adrenaline sequence. The time slows down as the bridge begins to collapse. Run forward and grapple the hook to save Lara's life. Swing directly over to the next ledge and jump over.
A giant spider drops down, you should move side to side and repeatedly jump around to prevent it from knocking Lara off the edge. After it's dead, smash the Pot to the right to find the next Treasure.
Turn back around and face the pit. Go over to the right wall, and you will see a series of handholds. Climb these, and then lean away from the wall. Jump backwards to catch the wooden bridge support. You can pull up and walk along the beam, or you can shimmey across the beam to reach a small platform. Shoot down a few bats and pick up the Treasure.
Look back at the ledge where you killed the spider. Grapple the ring underneath the bridge support and step off the platform to hang from the cable. Turn left on the cable, swing, and jump over to the small, curved platform. Pick up another Health Pack to the right. Then climb onto the wooden platform to the left.
Step a little further in, and smash a few small spiders. Chimney jump up the sides of the alcove you're in to reach a ledge. Pull up and you will be in a dark tunnel.
Just ahead is another Treasure sitting in the shallow water. Go to the very back of the room and chimney jump up the narrow alcove. Grab the ledge and pull up.