The House Chimney and Camp 2
From Camp 1, continue up mixed terrain on snow and rock for 1,640 feet (500 meters) to Camp 2 at 21,980 feet (6,700 meters). The camp is usually set against a cliff on a shoulder. It can often be windy and cold here but it's safe from avalanches. On this section is the famous House Chimney, a 100-foot rock wall split by a chimney and crack system that is rated 5.6 if free-climbed. Today the chimney is fixed with a spider web of old ropes, making it fairly easy to climb. The House Chimney is named for American climber Bill House, who first climbed it in 1938.
The Black Pyramid
The imposing Black Pyramid, a dark pyramid-shaped rock buttress, looms above Camp 2. This 1,200-foot-long section of the Abruzzi Spur offers the most technically demanding climbing on the entire route, with mixed rock and ice climbing on almost vertical cliffs that are usually covered with unstable snow slabs. The technical rock climbing is not as hard as The House Chimney but its steep and sustained nature makes it more serious and dangerous. Climbers usually fix ropes up the Black Pyramid to facilitate climbing it and rappelling down.
After climbing 1,650 feet (500 meters) from Camp 2, climbers usually situate Camp 3 at 24,100 feet (7,350 meters) above the Black Pyramid's rock wall and below steep unstable snow slopes. The narrow valley between K2 and Broad Peak often acts as a wind funnel, channeling high winds through the gap and making the snow slopes from here to The Shoulder above avalanche prone. Climbers usually stash extra gear, including tents, sleeping bags, stoves, and food, on the Black Pyramid because they are sometimes forced to descend for supplies if Camp 3 is swept away by an avalanche.
Camp 4 and The Shoulder
From Camp 3, climbers quickly ascend steep snow slopes that range from 25 to 40 degrees for 1,150 feet (342 meters) to the beginning of The Shoulder at 25,225 feet (7,689 meters). This section is done without fixed ropes. The Shoulder is a broad, low-angle hump on the ridge that is covered by a thick layer of ice and snow. There is no exact place to erect Camp 4, the last established camp before the final summit push. Usually placement is dictated by weather conditions. Many climbers place Camp 4 as high as possible, lessening the elevation gain on summit day. The camp is between 24,600 feet (7,500 meters) and 26,250 feet (8,000 meters).