Big square-dance arrangement on an endless plain of gym-floor material. There were two deejays in the middle with a giant hard drive that was open, with a needle over the platter and a large phonograph speaker above their head broadcasting stuff they said on the mic along with music from the hard drive platter. The basic idea was that of a square dance, except instead of "allemand left" and the other instructions for that, there were assembly language instructions, and the music was much more diverse. Each genre of music seemed to corrispond to a different ISA.
Most of the people there were people I know to various degrees at CMU. The more systems-y CSfolk were largely following the instructions, the more theory-y CSfolk were generally playing with glowsticks (maybe some people were making physical objects out of the trails?), and non-CSfolk looked to be socialising.