Inside one of UPS's busiest days of the year, CNNMoney takes a look at the UPS Worldport in Louisville, Ky., the center of the company's international shipping operations. It's the size of 90 football fields, sorts 350,000 packages an hour and contributes 20,000 jobs to the local economy. CNNMoney took a peek inside their busiest shift: 11p.m. to 3a.m. a week before Christmas.