Skeletons began infesting the kingdom late October 25, 2010 (October 26, effectively) when The Dungeon Full Of Dungeons was replaced by The Dungeon Full Of Skeletons. The infestation spread to The Skeleton-Infested Mall of Loathing the next day, and to a number of other places the day after. This culminated in a final showdown on October 31 inside The Cannon Museum, where four one-time-only combat encounters occurred in a predetermined sequence.
Skeleton invaders will show up in larger groups with higher amounts of Monster Level active:
On the fifth day, the The Dungeon Full Of Skeletons and The Skeleton-Infested Mall of Loathing were left in ruins, as the skeletons spread to more unoccupied locations in the Right and Wrong Sides of the Tracks and Market Square. The Gigantic Superfluous Fountain became completely overrun by skeletons.
On the sixth day, The Cannon Museum was invaded by skeletons. Once cleared of skeletons, the museum was left in ruins as well.
Attempting to adventure here after October 30th via the "Last Adventure" link resulted in the message, "That's not a thing anymore."