SubTropolis is the largest underground business park in the US. It is located northeast of downtown Kansas City, across the Missouri River, and was developed by Hunt Midwest, a real estate company which started in the local asphalt and limestone mining industry, and carved out this mine. SubTropolis started leasing out space inside in 1964, and now has five million square feet of developed space, and plans to build out another nine million square feet. Inside are 4.5 miles of paved roads, 2.1 miles of rail spurs, 350 truck docks, 1,500 parking spaces, and around 50 companies that lease space, employing more than 1,000 people. Companies include Underground Vaults and Storage, which has a major commercial film archive inside; truck customization businesses; Hallmark Cards; and the US Postal Service. There is also a large data center, part of the SubTroplois Technology Center. Hunt Midwest has developed the space on top of SubTropolis, with vehicle auction and storage yards, trucking terminals, and the Worlds of Fun amusement park. Hunt Midwest was founded by Lamar Hunt, of the famous Dallas oil tycoon family, who is also the founder of the National Football League.