They left right before graduation to find Margo.
When all the clues were found and figured out, they all lead to a really creepy abandoned building with no name. This was before they left for the trip, too. In the abandoned building, there were something called "Troll Holes". Troll Holes are moderetly large holes in the walls that you could climb through to get to another room. There were no doors, no windows, and tiny, tiny, holes in the celing were the only source of light. Thanks to the rats and mice that ran around.