Joshua P. Rechnitz's main mode of transportation is his bicycle. Rarely does he take a cab or ride the subway. On Thursday, he announced a commitment to underwrite an indoor facility at Brooklyn Bridge Park that will inspire future cyclists and advance bicycling in the city. The cost: an estimated $40 million.

The gift is one of the largest ever made in support of New York parks. "It's breathtaking," said Ellen Ryan, a spokeswoman for Brooklyn Bridge Park.

The...