It's been on for 17 seasons. Why I can't stop watching.

Here's a fun little wakeup call: The Real World/Road Rules Challenge is wrapping up its 17^th season tomorrow night. That's right, 17: still too young to drink but plenty old enough to drive. It's just one season behind the most durable reality challenge series, Survivor, and three ahead of Emmy magnet The Amazing Race. It shows up twice a year, as predictably as Memorial and Labor Day, and it's just been renewed for four more seasons.

It's also the only reality challenge series that never gets old. In a genre that has made a fetish of sticking to formula, the Real World/Road Rules Challenge freshens up the franchise every season. Even the title sequences change each time around—and for this season, The Duel 2, it's a doozy. In an homage to host country New Zealand, the contestants stomp and flail and grimace and flap their tongues in an excruciating approximation of the Maori dance known as the Haka. You want to look away … and you just can't.

Now I'm the first to admit it: I'm too old for this show. At least, I should be. It's about a bunch of self-absorbed twentysomethings, for heaven's sake—the spawn of an incestuous liaison between the absurdly tenacious (and increasingly sleazy) The Real World and its own spinoff, the now-defunct Road Rules. But by rolling a soap opera, a reality show, and a sports event into one energetic, artfully edited bundle, it transcends its tawdry origins. The sleeper hit of MTV, RW/RR: The Duel 2 has been winning its time slot among its 12-to-34 target demographic on cable and broadcast, with its audience growing season to season (unlike The Hills, which has seen its numbers drop).

Each season, around two dozen cast members from the twoparent shows—equal numbers male and female—are jetted to an exotic locale and bunked up together in a Real World-style luxury pad. All the requisite reality TV stereotypes are present and accounted for, often in multiples: the psycho, the good guy, the gay, the lesbian, the bisexual, the minority, the meathead, the drunk, the asshole, the bitch, the sweetheart, the floozy—even the cancer survivor. The usual frat-house shenanigans ensue—everyone parties, vomits, fights, hooks up, and behaves as badly as humanly possible.

So far, so formulaic. The twist is that each morning, hangovers be damned, these players have to make the unlikely transformation from party animal to warrior. Each one is either a repeat player—a "veteran"—or drafted onto the show from the most recent Real World installment—a "rookie." Different themes are rotated from season to season—Battle of the Sexes, the Inferno, the Gauntlet, the Duel—each determining the mode of combat and team formats, which vary from men vs. women; "Good Guys" vs. "Bad Asses"; veterans vs. rookies; or, as in this season's The Duel 2, no teams at all. Players compete in a series of extreme challenges that result in elimination playoffs so brutal, they'd make an American Gladiator weep.

Elimination rules also get switched up season to season. (It gets confusing, but you quickly learn to just go with the flow.) These changes work to shake up the natural patterns of dominance—veterans ganging up on rookies, males picking off females, meatheads freezing out the gays. One game-changing maneuver was Season 12's Fresh Meat challenge, when veterans were forced to partner up with complete newcomers, throwing off alliance patterns carried over from previous challenges.