This 7km-long white-knuckle adventure combines hiking, climbing over smooth rock slabs alongside waterfalls, ziplining over a surging river and navigating wild canyons via bridges and metal rungs.

BBC: North America by cable and bridge

Initially, it is a soft, foul-smelling matter that floats on the ocean but through exposure to the sun and the salt water over years it turns into a smooth lump of compact rock which feels waxy and has a sweet smell.

BBC: Rare whale vomit found on Morecambe beach

The car was rock solid and smooth sailing at highway speeds, with the ability to leap fairly athletically from one lane to another when called upon.

FORBES: Rolls-Royce Ghost Review: The Spirit is Willing

These dice are put through rock tumblers that give them smooth edges and a shiny finish, so they look great.

FORBES: The Epic 20,000 Roll Dice Randomness Test

Over the centuries, the river had slowly carried away mountainsides, tumbling and cracking rock, reducing boulders into a rainbow of smooth, flat stones the size of a child's hand.

CNN: The seven stones of simpler living

Swathes of what should be one of the best tourist roads in the country, leading to the Masai Mara reserve, one of Africa's finest game-viewing sites, are barely better than a rock-strewn, muddily rutted farm track that was once smooth tarmac.

ECONOMIST: Kenya

Hungry Bird, once billed as Clem Snide's swan song, is a sprawling bit of post-apocalyptic prog-rock, while The Meat of Life polishes its predecessor's weird edges to a smooth and appealing shine.

NPR: Exclusive First Listen: Clem Snide