The physical feature that allows people to travel through the mountains between Afghanistan and Pakistan is the Khyber Pass.

The Khyber Pass is a historic mountain pass that connects the Kabul Valley in Afghanistan to the Peshawar Valley in Pakistan. It's a narrow, winding route through the Spin Ghar Mountains, and for centuries it has been a crucial trade route and a strategic military route between the two countries.

While the Khyber Pass is challenging to traverse due to its steep slopes, narrow passages, and potential for danger, it's been a vital connection between Afghanistan and Pakistan throughout history.