Getting a lesson in retail inside world's busiest Costco The Iwilei Costco - the largest among the company's three Oahu locations - posted $300 million in sales last year. Iwilei is so busy, in fact, that it turns its entire inventory every two-and-a-half to three weeks... a logistical wonder considering most everything comes in by water. in Public bookmarkswith costcohawaiiretailwalmart