There was a time, in many villages and cities, that many buildings had tunnels underneath and still do. In the days of coal furnaces, many streets had scuttle holes to receive coal. The tunnels primarily were for businesses to be able to rely on neighboring businesses. I hate to think of the numbers of children who have been smuggled, stored, and transferred in unwitting businesses. There are also places that still have abandoned railroad tracks. How do you keep a hostage safe? Take the hostage out of the equation. Precious cargo -safer at home with their parents.