They are virtually impassable … to those who don't know them well.
"The Taliban knows the terrain," said John Nagl, of the Center for a New American Security. "They are able to use mountain passes that we are simply unaware of … that only very local people know."
In the south there are scorching deserts. Daytime temperatures can reach 120 degrees near Jalalabad. Blinding sandstorms can last for days and bring travel to a standstill.
For the Afghan people, life can be as challenging as the land. Nearly three-quarters of Afghans are illiterate. More than half live in poverty. All of them want stability.
"You have all Afghans wanting and praying and hoping for a decent central government, which will govern all the ethnic groups equitably," author and journalist Ahmed Rashid said. "It wants modernization."
And the water and tools needed to grow crops. Right now, poppies - used to make heroin - account for 60 percent of the country's economy and funnel as much as $100 million a year to the Taliban.
Cutting off that cash flow - without cutting off income to farmers - is a challenge as daunting as the mountains themselves.
"We have to restore the irrigation systems, we have to build more roads so that farmers can get goods to market," Nagl said.
No easy task as fighting continues to tear apart a country that already has so many battle scars.