I found these pictures online once upon a time and it's something I've always wanted to do, hoped to do it in the city, but with no grass, I don't think it would quite work out, ha.
You simply start with an old wagon wheel. I know, I know, where DO you find one of THOSE? Craigslist maybe? Some small town thrift store?
Once you have one, lay it down on the ground where you want your herb garden to be. If necessary, you can remove spokes to create bigger spaces.
Wagon Wheel Herb Garden up close, photo origin unknown
Then you dig out the grass, if you are laying it on grass of course. Or dig out the dirt or whatever is under the soon to be planting area.
Lay the wheel down, and you're done! Simple as that.
Wagon Wheel Herb Garden, photo origin unknown
Just plant your favorite herbs in each "section" and you've got not only a perfectly laid out herb garden, but a great conversation piece as well. It's hard to tell in this picture, but it really does look pretty cool when you're done. It's a bit more "formal" than just a free form garden, but for a courtyard or small space, it's a great solution to keep your herbs in one spot, contained, and organized. I can't wait until we can do one ourselves.