The W. B. Thompson Mansion, also known as Alder Manor, is a historic home located on North Broadway (U.S. Route 9) in the Greystone section of Yonkers, New York, United States.

At the turn of the century, large riverside estates characterized much of Yonkers; today the Thompson Mansion is one of the few to have survived the city's 20th-century urbanization.

While the other buildings on the property were repurposed, the mansion fell into neglect and was looted until Tara Circle, an Irish American cultural organization, bought it from the city.

To raise money for its restoration, Tara Circle holds occasional events there and rents it out for weddings and filming for movies such as Mona Lisa Smile[3] and A Beautiful Mind.

On the opposite side of North Broadway is the South Westchester Executive Park with taller modern buildings.

The trailway along the Old Croton Aqueduct, a National Historic Landmark, passes through the woods next to the preserve on the steep slopes leading westward down to the river.

At the river itself are some modern high-rise apartment buildings around the Greystone station on Metro-North Railroad's Hudson Line.

[2] A brick terrace continuing the stone balustrade from the forecourt surrounds the building; there are loggias at the north and south ends.

Above them is an entablature and central arch flanked by oval windows and supported by a combination of pilasters and freestanding columns.

[2] On the opposite side, a broken pediment above the segmental arched main entrance is supported by engaged columns.

Doors of glass and wrought iron open into a vestibule with marble floors and terra cotta bas-reliefs.

The marble floors continue into the entrance hall, with a plaster ceiling designed by Thomas Hastings.

[2] The drawing room has walnut panelling and bolection molding with carved birds, flowers and swags around the fireplace.

An Italian-style coffered ceiling is in the music room, complementing its imported 15th-century Italian stone fireplace.

The dining room has French-style coffering; both it and the library have oak paneling and classically inspired carved white marble mantelpieces.

The basement den has been extensively remodeled, but it still has an Asian design and a Chinese decorative wood carving along the stair leading to it.

It was first used in that latter capacity as the mansion where Russell Crowe as mathematician John Nash drops mail off there in the 2001 film A Beautiful Mind.