Karakoram.
Began forming alongside the Himalayas, roughly 50 million years ago.
A landscape with a history.
A distinct range from the Himalayas proper, but built by the same underlying India–Eurasia collision, further north and west. Contains some of the most extreme, glaciated high-mountain terrain on Earth.
What makes it remarkable
K2 (28,251 ft), the world's second-highest mountain and widely considered the most technically difficult of the world's highest peaks to climb. Still actively rising, part of the same ongoing collision driving the Himalayas.
Another skyline. Another story.
Himalayas
Began forming approximately 50 million years ago; still actively rising today.
Andes
Formation began roughly 200 million years ago, with the modern range's major uplift occurring within the last 25 million years.
Rocky Mountains
Primary formation (the Laramide orogeny) occurred roughly 80–55 million years ago.