Huh. The Merc used to have (still has?) a "bring your kid to work" type event on Columbus Day. They even brought us into one of the pits—back when they were still regularly open for business—to do a mock derivatives trading session. I guess it had never occurred to me before that those pits were being used for real trades on the same day—or maybe the brick and mortar exchanges were open, just "online-only", on Columbus Day.