Hop down onto a snowy ledge on the other side of the opening. It's very dark here. If the PLS doesn't shed enough light, turn up the brightness either in-game or on your TV/monitor.
Just beyond the snowy ledge is a flowing stream of icy water. After a few moments, chunks of ice begin to float past. To get out of this area, you need to make your way upstream, hopping from chunk to chunk. There's a ledge midway along on the right, where you can stop if necessary.
This ledge is shown more closely in the screenshot above. The entrance to the monastery, where you're headed, is beyond this ledge also on the right.
There's also a silver reward (5/6) on the left bank opposite the opening leading to the monastery. If you're collecting rewards, make your way to that ledge first.
Then wait for a few closely spaced chunks of ice to float by and hop across the stream to the exit.
Some tips: You don't needn't rush, since the water isn't moving that quickly, but try not to float farther downstream than the starting ledge. If you do, Lara crashes into the low tunnel opening and dies. If you make it only partway to the exit and run out of ice to jump on, float a short distance downstream, jump off on one of the ledges and wait for more ice chunks to come. Then try again.
[Part 1 | Return to the Nepal Walkthrough]