First off: a short glossary which will help you later:
A question that is hardly, if ever asked is "what is a dragon?" We all know what a dragon is: it is far easier to define what a dragon is NOT. For the most part, dragons are most often based upon snakes, but I have found no satisfactory definition for dragon.
A dragon is a creature that reaches out, grabs your soul, enraptures and frightens it, and when it leaves, you are left with a feeling of awe, fear, and respect that only a dragon can give. For some, only the fear lingers. For others, like me, the dragon never parted from the soul. We all know what a dragon is. If you stop a random person on the street and ask them a) what is a Degu? and b)what is a dragon? They could tell you what a dragon is, even though it is 'nonexistant' whereas they couldn't tell you what a Degu is, even though it is a real animal (it's a furry rat looking thing). Dragons have made a far reaching cultural impact on the human race that no other person or symbol can*.
Sometimes the line between dragon and snake is very thin. For example, I consider Kakuru a dragon. Kakuru is a rainbow serpent of the Aboriginal Dream Time myth whose appearance marks the beginning of the rainy season. "So, it's a big snake? What makes it a dragon?" First off: it's association with water. Not untill recently have dragons actually been linked to fire. Since the beginning, dragons have been aquatic beings. Secondly: it's magical significance. Dragons have long been associated with magic and the keepers of knowledge. On that note, Kakuru also fits the knowledge requirement in that it presents the knowledge of the coming rain season. Kakuru can be seen as a type of Wyrm: a dragon without limbs.
Today, there are more dragons than ever before. Recently, chinese dragons have become the latest fashion statement (Check out Miller's Outpost, Wet Seal, or the Delia's Catalogue and you'll see). And of course, if you're daring enough to take the plunge into the Sci-Fi/Fantasy section of your local Bookstore, as scary as it may be with all those Trekkies and Dungeons and Dragons creeps milling around, you can actually find some entertaining reads.
Of course, dragons don't really exist, right? I mean, no one has ever really seen one, right? And there's no scientific proof! Where are the bodies? The way I see it is as such: how can just about every human civilization share an image of a similar creature and it NOT exist? There are several theories which try to explain the existance of dragons:
There is the theory put forth by the late Dr. Carl Sagan that dragons are simply the genetic memory of dinosaurs, ingrained on our tree-dwelling mammalian ancestors, and that they represent a long standing animosity between reptiles and mammals.
On the opposite pole COMPLETELY is what you'll find in D.J Conway's book Dancing with Dragons. According to Condway, dragons used to live on earth, but retreated to the astral plane to escape the dangers of mankind, and that they can still be contacted, and occasionally visit.
I don't personally have an opinion, but I find it unlikely that they can breathe fire, but anywayz: these and more dragons inside these passages...Enjoy Dragons'Orb!