WHAT: Solomon R. Guggenheim Museums.

WHERE: Bilbao, Spain; New York.

WHY GO THERE: Sharing the same first name and mesmerizing architectural visions, Frank Lloyd Wright and Frank Gehry each designed a Guggenheim wonder. Both museums are giant sculptures in their own right; unearthly forms blending art and architecture in stop-in-your-tracks buildings.

Designed by Frank Gehry and completed in 1997, the boat-shaped Guggenheim of Bilbao soars above the gritty industrial Spanish port. The titanium skin changes color with the sun, to gold, silver or sky blue. Billowing curves catch and reflect the light with no two building aspects the same. As much a product of the technological era as Gehry's creativity, the museum's final edifice required computer modeling perfected for the aerodynamic bodies of jet aircraft.

The Guggenheim of New York, designed four decades earlier by Frank Lloyd Wright, presented such a construction challenge that a highway contractor who specialized in winding cantilevered rampways was called in. Outside, the cork-screw-shaped building is a standout against Manhattan's linear skyline. Inside, visitors take a dizzying spiraling trip up a six-story, quarter-mile concrete walkway, viewing Brancusi, Braque, Chagall, Kandinsky, Picasso, van Gogh and other modern treasures along the way. Daylight streams into a central rotunda through the roof's giant skylight.

Described as "ultra-modern cathedrals of culture" visitors come from around the world; some to see the art inside, others simply to marvel at two of the most fantastic and costly monuments of our age (the Guggenheim of New York cost $50 million; the Guggenheim of Bilbao, $100 million).

Other Guggenheim collections are the Guggenheim Hermitage Museum in Las Vegas and the Peggy Guggenheim Museum in Venice, Italy.

Sixty years after his death, Solomon Guggenheim's mission to further public appreciation of modern art continues to move forward. Guggenheim Abu Dhabi under construction on Saadiyat Island, in the United Arab Emirates, is part of a $27 billion arts complex to be completed by 2011. The architect is Frank Gehry.

If you go: The Solomon R. Guggenheim Museum in New York is at 1071 Fifth Ave. (at 89th Street), 212-423-3500. Open Saturdays to Wednesdays, 10 a.m. to 5:45 p.m.; Fridays, 10 a.m. to 7:45 p.m.; closed Thursdays. www.guggenheim.com.