I've seen it described many ways, one's internal sanctuary, one's temple, etc. Many athletes promote it as visualization. It may be part of the place Namaste refers to, depending on your opinion.
The dojo of the Soul is a powerful place, where you can work on anything. You can develop your soul aikido or your inner peace; you may find it a good place to hold your imaginary conversations or to take a peek at your past lives. I often practice my kung fu when I'm in my dojo.
The easiest way to create your dojo is to get yourself into a meditative state, however you usually do that (if you usually don't, try to do such things first, before tackling such a large visualizing project). If you want, you can visualize an area or environment for your dojo. It can be whatever you want, whatever makes you comfortable (inside, outside; what kind of lighting/weather; colors. Go nuts, whatever does it for you). Mine consists of a simple small rock altar, with a candle in the center and a single stick of incense, at one end of a clearing in the woods (packed-earth flooring).
"Now what?" you ask? Well the simple answer is I don't know. Do whatever you want; it all depends on what you wish to accomplish. And if perchance I wander into your dojo, please don't unleash your Wu-Tang Style upon me :)