tradition, sometimes known as Senior Ditch Day
The whole thing started when Senior Ditch Day was just one day during the year when all the seniors took off for the beach, relaxing and decompressing. The underclassmen, not a sympathetic bunch, would break into the seniors' rooms and leave little pranks, another Caltech tradition. Eventually, the seniors started putting barricades on their doors before leaving in order to keep the pranksters out. The underclassmen, not to be deterred, would find ways through the barricades and prank the rooms. Needless to say, this started to escalate as the years went by. The barricades became more and more sophisticated. People would put up walls of concrete over their doors and leave ... and the underclassmen would pull out sledgehammers, borrow equipment from physical plant, do whatever it took to break in. The barricades then started to evolve in a different direction. Now called 'stacks', the barricade could be removed by thinking, rather than by brute force. As an example, I can briefly describe one stack that made it into Caltech lore - the Apocalypse Now Stack. The door to the senior's room had a peephole in it. Usually people in groups of ten or so would work on solving a single stack. The challenge here was to operate a remote controlled helicopter inside the room which had a scoop hang from it. If they navigated the helicopter over to pick up a ball and then dropped the ball into a hole setup in a box in the middle of the room, then a device would unlock the door, allowing the group entry. A couple of things made this more complicated, however. The remote control was attached to a wire which ran out the back room of the window which was covered to make it opaque. So, somebody got a ladder and climbed up to the back window and operated the remote control, and listened for instructions from the person in the front looking through the peephole. However, the moment the helicopter was activated, the Ride of the Valkyries started playing at full volume! Needless to say, this made communication much more difficult, and the group of ten people had to form a fire brigade to pass instructions from the peephole to the operator at the window. Eventually they were successful and gained entry into the room. Now, seniors not wanting their room to be pranked, would then leave a bribe in the room, usually food or beer. If the underclassmen took the bribe, which they usually did, then they were under the honor code not to leave a prank.
Ditch day is now an established, and enjoyable tradition at Caltech. Seniors spend months and months developing puzzles, constructing stacks, saving up for bribes. The underclassmen look forward to it as well, because it is an automatic day off from classes for them too, as it often takes the entire day to solve many of the stacks. The actual date of Ditch Day is kept a secret from the underclassmen, and only administration is notified ... as are professors, so that they are not baffled when their classes are empty that day. The campus takes on a carnival like atmosphere and the media usually does a story on it.
There are currently three major kinds of stacks:
Brute Force Stacks: which usually entail lots of sledgehammers and equipment. There are practical limits to how difficult these can be without doing structural damage to the building.
Finesse Stacks: These stacks require you to solve puzzles and come up with creative ways to break into the room. Often, the senior has come up with a single way to break his or her stack.
Honor Stacks: The newest of the three types of stacks. This stack is more of a role playing stack, often mixing elements of brute force and finesse. If you agree to work on a particular senior's stack, he or she will ask you to do things such as "dress up in a cape and tights and ask Professor So and So for a key to get you to the next stage of the stack". This is the 'honor' component, that you play along with the stack's storyline.
One other facet of Ditch Day is that seniors cannot be on campus between 8 am and 5 pm during that day. Any seniors found will be bound with duct tape to the nearest tree and left their until 5 pm. This prevents seniors from meddling with the stacks ... making it a challenge for the stack to go smoothly on its on.
All in all, Ditch Day is one of the most enjoyable traditions at Caltech. Its fun for both underclassmen and seniors. Sure, I nearly failed my classes senior year because of all the time and work I put into my stack ... but it was worth it.