Industrialist Andrew Carnegie (1835-1919) sought comfort more than show when he built this 64-room house, designed by Babb, Cook & Williard, on what were the outskirts of town in 1901; this was the year he became the richest man in the world, and from the first-floor study Carnegie administered his extensive philanthropic projects. (Note the low doorways -- Carnegie was only 5 foot 2 inches tall.) The core of the museum's collection was assembled in 1897 -- not by Carnegie -- but by the two Hewitt sisters, granddaughters of inventor and industrialist Peter Cooper. Major holdings focus on aspects of contemporary and historical design, including drawings, prints, textiles, furniture, metalwork, ceramics, glass, woodwork, and wall coverings. Selections from the permanent collection are on view in the recently opened Nancy and Edwin Marks Gallery. Changing exhibitions -- which have covered such subjects as jewelry design and the construction of the Disney theme parks -- are invariably enlightening and often amusing. In summer some exhibits make use of the museum's lovely garden. COST: $10 general; $7 for seniors and students; free for members and children under 12. Subway: 4, 5, 6 to 86th St.