Jay Michaelson’s take on the famous event held each year in the Black Rock Desert, Nevada:

You don’t get it. You don’t get what it’s like to have 50,000 people circle around a wooden effigy, with 1000 people spinning fire and 500 more playing drums, all encircled by 200 art cars — and then all roaring in unison as the effigy is set afire. You might think you get it, and it may scare or tempt or delight you, but I assure you, you don’t get it. None of us do, because it’s not about any one thing in particular; “it” can be an orgiastic celebration, or the sad mourning of a lost loved one. Or a warm, hippie-like community. Or a mean, Mad-Max-like apocalypse. “It” is chiefly a space in which all these things are possible.

The temporary erasure of societal, social, and personal boundaries is, for most of us, terrifying. Such boundaries help build the structures of society and self; they give form to human life, which is often chaotic and unpredictable. Thus they have been the bedrock of religious and civil life for millennia, even before the Furies were imprisoned under Athens, and Moses descended from Sinai.

But if religion creates boundaries, mysticism and spirituality efface them. In the transcendence of ordinary distinctions, peak experiences such as those encouraged at Burning Man give a glimpse of the ultimate, the infinite. It may seem absurd to suggest that Burning Man is a mystical event. But then, if it’s just a big party, why is there a temple in the middle of it?

More here. Is that the whole truth? Check out a contrasting view in the comments section. I have never attended myself.
(Photo sources: one, two, three)