You've probably heard about these two the last couple weeks. They are attempting to be the first team to free climb (climbing without using gear to ascend past sections) the Dawn Wall on El Cap in Yosemitie. For reference the hardest single pitch ever climbed is 5.15c. The Dawn Wall route has six pitches rated in the 5.14 range, with two rated 5.14d, just 3 steps below the hardest single pitch anyone has ever done.
You can watch the last push here and history in the making.
They just finished up pitch 30 and swung leads and Tommy Caldwell is starting up pitch 31. (EDIT: Actually they're starting up the final pitch!!). There are 32 pitches total.