If you've ever taken a tour of the US Capitol, you may have noticed the tiny doors in some of the rooms of the building. Many visitors ask about them. No, they are not doorways to the chambers of a rodent legislature, and no, they are not fairy doors.
This little videos explains their origins. Spoiler alert: They have spigots behind them that could be used as fire hydrants and they provided water for washing the floors.
H/t Don Webb