What is the hardest mountain to climb? Is it the tallest, the steepest, the one with the slipperiest rock walls or the fewest handholds? The one with the harshest weather? There are a lot of different factors that go into determining the difficulty of a climb. To a large degree, difficulty is a subjective measurement. But we can still come up with a list of challenging climbs based on a combination of these factors as well as the reports of climbers who have actually tackled these giants.

10. Annapurna

9. Mount Khuiten

8. The Matterhorn

7. Mount McKinley

6. Fizroy and Cerro Torre

5. Mount Blanc

4. Kanchenjunga

3. Nanga Parbat

2. Mount Everest

1. K2

Since difficulty is a subjective quality to gauge, many climbers debate which of these mountains is the toughest to ascend, but each of them undeniably poses extreme challenges. If you ever make it to the top of one of these mountains and back alive, consider yourself extremely accomplished—and possibly very lucky as well. Many of the factors which impact these climbs are unpredictable and uncontrollable. Climbing any one of these peaks is a test not only of courage, but also of luck as well as the ability to adapt to sudden change.