The Allison Mansion anchors the 64-acre Riverdale estate. The exterior of the mansion, designed by Indianapolis architect Herbert Bass, is an eclectic blend of early Prairie School and Lombardy Villa architecture and is located on the top of a bluff overlooking the meadow and lakes below. Dubbed the “House of Wonders,” the Allison Mansion contained many state-of-the-art conveniences including an elevator, a central vacuum system, a telephone intercom system, automatically lighted closets, pumped-in ice water, an indoor swimming pool, and the sophisticated indirect lighting systems favored by Frank Lloyd Wright.
James Allison hired William Price, of the Philadelphia firm of Price and McLanahan, to complete the interior. The interior is lavishly designed in traditional European designs. The 40' x 40' great foyer is done in a high Renaissance style with elaborately carved Circassian walnut woodwork (now extinct) and a one-ton German silver chandelier. The library is designed in the Gothic style, with gilded carved leather panels and a Rookwood fireplace. The small reception room reflects the era of Louis XVI and features embroidered silk wall coverings. The music room features a delicately carved white mahogany organ screen, and the card room on the lower level has a finely detailed hand-painted gilded mural depicting The Three Musketeers in the form of James Allison, Carl Fisher, and Frank Wheeler. Finally, the aviary is a large glass-enclosed space executed in white Italian marble with intricately detailed balustrades and newel posts and a Tiffany-style art glass ceiling. To produce this wide range of styles, Allison imported both materials and craftsmen from Europe.