Okay, first let's define Hypertufa. According to The Artistic Garden, Hypertufa (hyper-toofa) is an artificial stone that was 'first created in the mid 19th century by mixing sand, peat, various volcanic aggregates and cement.' It's lighter than stone or concrete and if cured properly it's freeze-proof. Now to the fun part: Using hypertufa to make pots. Here's a video showing us how.
But wait! Hypertufa can be used to make more than garden vessels. Here's a list of inspirational projects that will make you want to wheel out the wheelbarrow. The hollowed out spheres are especially fabulous! (There's an irritating pop-up on the site, but it's worth the interruption.)