A storied, waterfront beach mansion at 66 Seafield Lane in Westhampton Beach South is finally in contract.

It last asked $16.75 million — less than half its original $39 million asking price in 2008. The 16,000-square-foot home sits on 6.86 acres. It was designed in 1903 for coal baron William Atwater by Henry Bacon, the architect who designed the Lincoln Memorial in Washington, DC.

The nine-bedroom, nine-bathroom home comes with six fireplaces, a large entryway with a three-story staircase, a living room with a fireplace and a banquet-size formal dining room with a fireplace and hand-painted murals, according to the listing.

The home also features a gourmet kitchen, a billiards room, sunroom and office — along with a carriage house with “century-old grape vines” and catalpa trees.

There are also “formal gardens, rolling lawns,” a greenhouse, a pool and a deep-water dock.

The sellers are Kathryn and Len Conway.

Douglas Elliman’s Enzo Morabito, who had the listing, declined to comment.