Dallas, Texas is getting a lot greener.

Credit: Michael Van Valkenburgh Associates

This story originally appeared on BusinessInsider.com.

The city is building a 10,000-acre nature district — nearly 12 times the size of Manhattan's Central Park — along the Trinity River. Featuring plenty of trees, walkways, sports fields, and flora, the site will become the largest urban park in America.

In late October, Annette Simmons, the widow of late billionaire Harold Simmons, donated $50 million toward 285 acres of the ongoing project. Set to be complete by 2021 and cost $250 million, this portion will be called the Harold Simmons Park. Dallas Mayor Mike Rawlings expects other private donations to fund the rest of the Harold Simmons Park, according to Dallas News.

It will become part of the larger nature district, called the Trinity River Project, that began in the early 2000s. In total, the city has spent over $609 million to build trails, a bridge, a horse park, a golf course, and a community center in a 7,000-acre forested area outside Dallas as of 2015. In the future, there are also plans to build shops, restaurants, housing, and offices near the river.