The Gulag - Climbing into the Building

Stand near the rope-wrapped post...

...and shoot a rope line into the rope-wrapped beam above.

Climb the line...

...and drop down on the landing at the top of the broken staircase.

Jump up to grab the nearest windowsill. Climb then jump to the right to grab the next narrow ledge. Scramble up the wall to grab the white molding above.

Then traverse around the corner until Lara is hanging in front of the open window.

Drop and grab the window sill, then climb in to meet up with Jacob.