One of Hawaii’s largest private landowners is seeking to sell its vast collection of real estate, including the core of downtown Kailua.

The Harold K.L. Castle Foundation through its asset management arm, Kaneohe Ranch Co., has retained the investment brokerage firm Eastdil Secured to sell more than 600 acres in Hawaii and almost 100 acres on the mainland, according to the investment offering.

Eastdil touts the portfolio as a “once-in-a-lifetime opportunity” to own a “phenomenal” collection that includes shopping centers, land leased to businesses and the 38-acre town center of Kailua that includes land under Foodland, Safeway, Whole Foods, Times and Macy’s.

Eastdil also said there is an opportunity to redevelop much of Kailua’s commercial center because several land leases there expire this decade.

Mitch D’Olier, president and chief executive officer of Kaneohe Ranch, issued a written statement describing the sale offer as part of a “variety of strategic alternatives” for the Castle Foundation.

“These options may include selling some or all of the owners’ real estate holdings in Hawaii and elsewhere, or retaining ownership of some or all of the real estate,” he said. “No decision has yet been made concerning whether any of these holdings will be sold.”

D‘Olier, through a spokeswoman, said he would not comment further.