Zion National Park, Utah, USA

Rocky heights. Squeezing into the Narrows

When Zion National Park, in the US state of Utah, was established way back in 1919, poor roads and a lack of trails meant it attracted fewer than 2,000 visitors. These days, it has the opposite problem, with more than four million visitors each year crowding into popular areas such as the Narrows, the narrowest section of Zion Canyon. The gorge, with walls 1,000ft tall, can be seen from a paved path but many people like to experience it up close, wading through the Virgin River.

In recent years, Zion has moved ahead of Yellowstone and Yosemite to become the fourth most-visited US national park (Great Smoky Mountains, the Grand Canyon and Rocky Mountain parks are the top three respectively). It's also part of the Grand Circle, a region that includes parts of five states and is the most concentrated area of national parks and monuments in the US.