With more than 4 million miles of pavement on US roads, travelers are faced with an abundance of scenic routes from sea to shining sea. And with 63 parks in the national park system, many of those roads zip straight through some of America’s finest landscapes. But which roads are the finest? We spent a summer driving across the country to find out. These are the most drivable national parks in the US.

The gates of Rocky Mountain National Park sit less than two hours from Denver, Colorado, making this western 415-square-mile fortress one of the most accessible parks in the country. That shouldn’t deter travelers looking for unparalleled views, though, as Rocky Mountain serves up a surreal, tundra atop America’s highest tarmac: Trail Ridge Road.

Trail Ridge Road carries drivers 48 miles west from the city of Estes Park, across the Continental Divide and into the town of Grand Lake. At 12,183 feet, the road's highest point is often a swirling dreamscape of shifting clouds, spitting snow and wandering elk.

The most popular time to visit Rocky Mountain National Park is during the elk rut from mid-September through mid-October, so plan accordingly. However, regardless of when you venture to Rocky Mountain National Park, the sky-high views are unrivaled.

There’s no stretch of American asphalt quite like Glacier's Going-to-the-Sun Road. The perilous, 50-mile highway in Montana tattoos a path along the bones of North America's geologic foundations, putting drivers face-to-face with death-defying views of a prehistoric glacial valley. The path here is precious, often opening by June or July and remaining fully passable for just a few months, as the snow can pack back in by October.

Going-to-the-Sun Road is an unmissable experience. Travelers who want to ditch the crowds can leave the pavement for one of Glacier’s many loose gravel roads that dot their way through unblemished wilderness — and equally impressive views — near the outpost of Polebridge, Montana, (pictured), and the Canadian border.

You won't escape the crowds at Great Smoky Mountains National Park, which is often open year-round due to its lower elevations and southern location on the Tennessee/North Carolina border. However, you'll still find plenty of natural beauty cruising through the heart of one of America’s most ancient mountain ranges. Autumn views here, in particular, are hard to top.

Geologists say the Appalachian Mountains are at least four times older than the Rocky Mountains. These mountains have been aged like a fine, geologic wine, leaving travelers with sweeping panoramas of soft, rolling peaks that melt into the early morning fog and glowing afternoon sunsets.