Myrtillocactus geometrizans - Bilberry Cactus
Myrtillocactus is a fast-growing candelabra-shaped cactus that grows 15' tall. And it's blue, glowy blue, and makes magenta berries so sweet that they're grown as a crop in Mexico.
Bilberry Cactus is fast growing and is often used as grafting stock. You may never have seen one, because it's so easy to grow that collectors don't bother. Go figure. With favorable conditions it can reach heights of 15 feet, an impressive, architectural specimen with creamy white flowers, sweet berries, and minimal prickers.
Myrtillocactus comes from Northern Mexico, needs the warmth of zones 9-10, full sun, fast draining soil, occasional water. It starts blooming when it is only 2' tall, but will remain unbranched for many years. In cold zones, a sunny windowsill will do just fine.