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David spends twelve hours a day as a swashbuckling explorer in a subterranean world of dungeons and elves. He plays a character called Lotsu. He should be in class getting A grades. Instead he has succumbed to the latest fad sweeping college campuses: total immersion into multiuser fantasy games.

Multiuser fantasy games are electronic adventures run on a large network fed by university and personal computers. Players commonly spend four or five hours a day logged into fantasy worlds based on Star Trek, the Hobbit, or Anne McCaffrey's popular novels about dragon-riders and wizards.

Students like David use school computers, or their own personal machine, to log onto the Internet. This mega-network, now collectively funded by governments, universities, and private corporations around the world, subsidizes all ordinary passengers traveling across it. Colleges freely issue Internet accounts to any student wanting to do "research." By logging on from a dorm in Boston, a student can "drive" to any participating computer in the world, link up for free and stay connected for as long as he or she wishes.

What can one do with such virtual travel, besides downloading papers on genetic algorithms? If 100 other students were to suddenly show up in the same virtual place, it might be pretty cool. You could: throw a party, devise pranks, role-play, scheme, and plot to build a better world. All at the same time. The only thing you'd need is a multiuser place to meet. A place to swarm online.

In 1978, Roy Trubshaw wrote an electronic role-playing game similar to Dungeons and Dragons while he was in his final undergraduate year at Essex College in England. The following year, his classmate Richard Bartle took over the game, expanding the number of potential players and their options for action. Trubshaw and Bartle called the game MUD, for Multi-User Dungeons, and put it onto the Internet.

MUD is very much like the classic game ZORK, or any of the hundreds of text-based adventure video games that have flourished on personal computers since day one. The computer screen says: "You are in a cold, damp dungeon lit by a flickering torch. There is a skull on the stone floor. One hallway leads to the north, the other south. There is a grate on the grimy floor."

Your job is to explore the room and its objects and eventually discover treasures hidden in the labyrinth of other rooms connected to it. You'll probably need to find a small collection of treasures and clues along the way in order to win the motherlode booty, which is usually to break a spell, or become a wizard, or kill the dragon, or escape the dungeon.

You explore by typing something like: "Look skull." The computer replies: "The skull says, 'Beware of the rat.'" You type: "Look grate" and the computer replies: "This way lies Death." You type: "Go north," and you exit through the tunnel on your way into the unknown in the next room.

MUD and its many improved offspring (known generically as MUDs, MUSEs, TinyMUDs, etc.) are very similar to classic 1970s-style adventure games but with two powerful improvements. First, MUDs can handle up to 100 other human players immersed in the dungeon along with you. This is the distributed, parallel characteristic of MUDs. The others can be playing alongside you as jolly partners, or against you as wicked adversaries, or above you as capricious gods creating miracles and spells.

Secondly, and most significantly, the other players (and yourself) can be at work adding rooms, modifying passages, or inventing new and magical objects. You say to yourself, "What this place needs is a tower where a bearded elf can enslave the unwary." So you make one. In short, the players invent the world as they live in it. The game is to create a cooler world than you had yesterday.

MUDs then become a parallel, distributed platform for a consensual superorganism to emerge. Someone tinkers up a virtual holodeck for the heck of it. Later, someone else adds a captain's bridge and maybe an engine room. Next thing you know you have built the Starship Enterprise in text. Over the course of months, several hundred other players (who should be doing calculus homework) jack in and build a fleet of rooms and devices until you wind up with fully staffed Klingon battleships, Vulcan planets, and the interconnected galaxies of a StarTrek MUD. (Such a place exists on the Internet.) You can log on at any time, 24 hours a day, greet fellow members of the crew -- all in role-playing characters -- to collectively obey orders broadcast by the captain, and battle enemy ships built and managed by a different set of players.

The more hours one spends exploring and hacking the MUD-world, the more status one earns from the rulers overseeing that world. A player who assists newcomers, or who takes on janitorial chores in keeping the database going, can earn increasing rank and power, such as being able to teleport for free or being exempt from certain everyday laws. Ultimately every MUDer dreams of achieving local god or wizard status. Some become better gods than others. Ideally, gods promote fair play, keep the system going, and help those "below." But stories of abusive and deranged gods are legendary on the Internet.

Real-life events are recapitulated within MUDs and TinyMUDs. Players will hold funerals and wakes for characters who die. There have been TinyWeddings for virtual and real people. The slipperiness between real life and virtual life is one of MUD's chief attractions, particularly for teenage kids who are wrestling with their identity.

On a MUD, you define who you are. As you enter a room, others read your description: "Judi enters. She is a tall, dark-haired Vulcan woman, with small pointed ears, and a lovely reddish tinge to her skin. She walks with a gymnast's bounce. Her green eyes seem to flirt." The author may be petite female with a bad case of acne, or she may be a bearded male masquerading as a women. So many female-presenting characters are actually males pretending at this point that most savvy MUDers now assume all players to be male unless proven otherwise. This has led to a weird prejudice against true female players who are subject to the harassment of "proving" their gender.

Most players live out virtual life with more than one character, as if they are trying out various facets of their persona. "MUDs are a workshop for the concept of identity," says Amy Bruckman, a MIT researcher who studies the sociological aspects of MUDs and TinyMUDs. "Many players notice that they are somehow different on the net than off, and this leads them to reflect on who they are in real life." Flirting, infatuation, romance, and even TinySex are as ubiquitous in MUD worlds as on real campuses. Only the characters vary.

Sherry Turkle, who calls the computer an occasion for a "second self" goes further. She says, "On a MUD, the self is multiplied and decentralized." It is no coincidence that a multiple, decentralized structure is the emerging model for understanding real-life, healthy human selves.

Pranks are also rampant. One demented player devised an invisible "spud" that, when accidentally picked up by another player we'll call Visitor, would remove Visitor's limbs. Others in the room would read: "Visitor rolls about on the floor, twitching excitedly." The gods were summoned to fix player Visitor. But as soon as they "looked" at him, they too got spudded, so that everyone would read, "Wizard rolls about on the floor, twitching excitedly." Ordinary objects can be booby-trapped to do almost anything. A favorite pastime is to manufacture a neat object and get others to copy it without knowing its true powers. For example, when you innocently inspect a "Home Sweet Home" cross-stitch hanging on someone's wall, it might instantly and forcibly teleport you home (while it flashes "There is no place like home").

Since most MUDers are 20-year-old males, violence often permeates these worlds. Elaborate slash-'n'-hack universes repel all but the most thick skinned. But one experimental world running at MIT outlaws all killing and has gathered a huge following of elementary and high school kids. The world, Cyberion City, is modeled on a cylindrical space station. On any one day about 500 kids beam up into Cyberion City to roam or build without ceasing. So far the kids have built 50,000 objects, characters, and rooms. There's a mall with multiplex cinema (and text movies written by kids), a city hall, science museum, a Wizard of Oz theme park, a CB radio network, acres of housing suburbs, and a tour bus. A robot real estate agent roams around making deals with anyone who wants to buy a house.

There is deliberately no map of Cyberion City. To explore is the thrill. Not to be told how things work is the teacher. You are expected to do what the kids do: ask another kid. As Barry Kort, the real-life administrator of the project, says, "One of the charms of entering an unfamiliar environment and culture such as Cyberion City is that it tends to put adults and children back on an equal footing. Some adults would say it reverses the balance of power." The main architects of Cyberion City are 15 years old, or younger. The sheer bustle and intricacy of the land they have built is intimidating to the lone, over-educated immigrant trying to get somewhere, or build anything. As San Francisco Chronicle columnist Jon Carroll exclaimed on his first visit, "The psychological size of the place, all those rooms, and the 'puppets' flitting about, makes it seem like being dropped into downtown Tokyo with a Tootsie Roll and a screwdriver." To survive is the only task.

Kids get lost, then find their way, then they get lost in another sense and never leave. The continuous telecommunication traffic due to nonstop MUDing can cripple a computer center. The college of Amherst outlawed all MUDing from its campus. Australia, linked to the rest of the world by a limited number of precious satellite datalines, banned all international MUDs from the continent. Student-constructed virtual worlds were crowding out bank note updates and calls from Aunt Sheila. Other institutions are sure to follow the ban on unlimited virtual worlds.

Until now, every MUD going (and there are about 200 of them) has been written by fanatical students in their spare time with no one's approval. A couple of pseudo-MUDs have a large following on commercial online services. These almost-MUDs, such as Federation 2, Gemstone, and ImagiNation's Yserbius permit multiusers but give them only limited power to alter their worlds. Xerox PARC is nurturing an experimental MUD running on its company computer. This trial, code-named the Jupiter Project, explores MUDs as a possible environment in which to run a business. An experimental Scandinavian system and a start-up called the Multiplayer Network (running a game called Kingdom of Drakkar) both boast a prototype visual MUD. The dawn of commercial profit-making MUDs in not far away.

Children of the 22nd century will marvel at Nintendo games of the 1990s and wonder why anyone bothered to play a simulation where only one person could enter. It's sort of like having one telephone in the world and no one to talk to.

The future of MUDs, then, converges upon the future of SIMNET, the future of SimCity, and the future of virtual reality. Somewhere in that mix is the ultimate god game. I imagine it as a vast world set into motion with a few well-chosen rules. It is populated by myriad autonomous critters and other creatures who are mere simulacra of distant human players. Characters unfold over time. Tangles grow.

Eventually the simulated world quickens with palpable energy as the interrelations deepen and the entities alter and shape their world. The participants -- real, fake, and hyperreal -- coevolve the system into a game different than it began. Then, the god himself dons a pair of magic goggles, suits up, and descends into his creation.

The god who lowered himself into his own creation is an old theme. Stanislaw Lem once wrote a great science-fiction classic about a tyrant who kept his world in a box. But another version predates it by millennia.