A climate milder than your own can be shocking: there, plants you may have known only on your windowsill are thriving right in the garden. More shocking: their sizes and habits are quite foreign to those back home.
For example, in New England, it's a surprise that any cacti at all survive, let alone enjoy themselves. They do—OK, not the fifty-footers you might see in Arizona—but, still, true cacti. Even under ideal conditions, though, few will ever grow higher than your kneecaps.
The picture below shows a tropical cactus that's the opposite of the ones hardy up north: it's a vine that can climb twenty to thirty feet into trees.
And—perhaps most important for this northern gardener—it can be grown as topiary.