Since starting the company, Cornell has noticed a steady increase in ­travelers. She's been to Bilbao 40 times, and she finds it, like all good architecture, to be a powerful experience every time. "As soon as people walk down the street and the Guggenheim comes into view, I just wish I had a video camera to watch," she says. "People will say, 'I never could have imagined it would be this great.' That's not me. That's Frank Gehry."

But her clients come for more than Gehry and from all over the globe - South America, the United Kingdom, and across the United States. The rise of the celebrity architect has prompted Cornell to coin a phrase for her most passionate clients: architecture groupies, individuals who focus on one high-profile architect and scour the planet for all of his or her creations. Cornell mentions a recent customer who sent in a page she'd torn from a magazine, which featured a bridge in the background. The customer believed the shape of the bridge suggested it was the work of Santiago Calatrava, a renowned Spanish architect known for his undulating creations, but she wanted verification. The note said: "Gail, I would have never noticed this before. I'm sure this is Santiago Calatrava. Can you confirm? I now look at everything completely differently." (Cornell confirmed.)

That kind of obsession and eye for a certain architect's work are characteristic of most of her travelers and evidence of the groupie mindset. "People will send articles, clippings, photos because they want to keep this architectural dialogue going," she says. The Calatrava fan will have much to chat about: Calatrava's current projects include bridges in Jerusalem, Dallas, and Venice; an 86-acre cultural center in Spain; a series of projects for the 2004 Olympics in Athens; and, most importantly, The World Trade Center PATH Terminal.