Hint: Stuck In Rock or In Mid-Air?
Occasionally Lara becomes hung up on her environment or atop some breakable jars. If she cannot jump out of her predicament, try having her duck (hold the crouch button) and see if she can nudge herself out of being stuck.
Cheat: Cheat List
These codes are from Tomb Raider: Legend, but work in Underworld as well.
* Invincibility - Hold L2 and press A, R2, Triangle, R2, Square, L1
* One hit kills - Hold L2 and press Triangle, A, Triangle, Square, L1, Circle
* Reveal enemy health - Hold L2 and press Square, Circle, A, L1, R2, Triangle.