Pretty capable for something that isn't on tank treads.
There has been a lot of hype about the 6X6 version of the Mercedes-Benz G-Class, but a lot of the pictures and video have shown it in urban areas, or at least on the road. And while this does show the vehicle's ability to impress, it doesn't really give much of an idea of what it's like off road, and this would seem to be the best reason of all to buy a 6X6 vehicle. So here is some video of one of these giant beasts crawling over some rocks in Tuscany, something is does with ease.
Unfortunately, the video will probably make you want to buy one, something you can't do now even if you live in a market where they were sold, as they're sold out.