WE'VE JUST FINISHED

breakfast in our Prague hotel room when the phone rings. It's the concierge, announcing grandly that our car has arrived. The second we step outside, a dapper chauffeur with a crew cut stops polishing the hood of the black sedan and rushes to open the back door. As we settle into the soft leather seat, Mrs. L nsk , our guide for the day, hands us a beverage and begins pointing out sites of interest as the driver deftly navigates the winding cobblestone streets. Is it our imagination, or are people staring? We feel like a jet-setter.

And for 500 bucks for four hours, we are.

Who says private tours are just for the rich and superrich? Once a fairly exclusive domain, this tiny niche of the travel business is attracting the merely well-off or at least travelers who want to feel that they are by indulging in a day or two of private touring. For $150 to $1,000 a day, tour guides ranging from freelance local-history buffs to licensed travel professionals are leading families, couples and even individuals on the same tours people take in those gigantic buses. Only now there's no need to share a glimpse of the Champs-Elys es or Rockefeller Center with 40 strangers, wasting time with bathroom breaks and slow walkers. While private tours sometimes follow a standard itinerary, many adapt to travelers' interests, from Paris shopping trips to tours of historic Scottish kitchens. The trend is toward customization, says Bob Whitley, president of the U.S. Tour Operators Association, because "boomers like to feel that they're in control."

Indeed, it's largely boomers taking these tours travelers with money and an expectation of having a unique experience under catered conditions. Michael Moshes, founder of Private-Guides.com and a pioneer in this business, reports that tour bookings have quadrupled in the past year. Artisans of Leisure, a New York-based company that arranges longer custom tours, says it's doubled its business every year since opening in 2003. One factor driving growth is more intergenerational travelers people like James and Devereux Socas of McLean, Va., who recently hired retiree John Sutton, a history buff, to lead them, their mothers and three young sons around Colonial Williamsburg. Sutton brought "color," they said, appealing to grandparents and kids alike.

But how do you find a reputable guide whose accent isn't too thick, whose driving record is clean and who knows more than a thing or two about those Scottish kitchens? Some countries require licensing, but that can be just an administrative rubber stamp, and hotel concierges don't hesitate to recommend an overpriced tour service or even their unemployed cousin. (Our concierge handed us a brochure focused more on the cars we'd be riding in than on the content of the tours a red flag.)

For our recent trip to Prague, we decided to hit the Web to plan three private tours: two all-day walking tours of the city's architecture and one driving tour outside the city. We discovered that all this specialized catering can be a mixed bag sometimes delightful, sometimes exhausting.

CHOOSING A GUIDE feels a lot like online dating. Looking for our special someone with whom to share a day of adventure, we canvass web sites like guidingprague.com and infohub.com, combing through bios and tour descriptions, eliminating any guide whose English seems shaky. Then we knock out any whose mug shot looks too youthful (history is better filtered through maturity, we speculate) or too dour (who needs cranky?). Despite his shaggy picture we gravitate to Petr Zidek, a civil engineer who specializes in architecture and Jewish history, and Joeri Happel, a Dutch expat who speaks six languages and promises a rich mix of history and contemporary culture. After digging up client testimonials, we email questions about the guides' licensing and expertise. We're not bothered by motley career histories; previous lives as street musicians and barkeeps lend an exotic air of life experience. What we're really sniffing around for is genuine passion for history and culture.

Petr and Joeri each tell us later that we saved significantly by contacting them online. By e-mailing Petr through InfoHub.com, which levies a 10% listing fee on the guides, we pay him $180 for a seven-hour walking tour, instead of $235 through a local tour service. And we should have shopped around for the driving tour. We found Mrs. L nsk (and chauffeur) through that brochure from our concierge. Tour operators often adapt prices to the class of hotel they serve; for our four-star boutique, the rate sheet listed a four-hour tour of nearby Terez n at $480. Through local service Prague Private Guides, we could've booked it for $330.

Ten minutes into our first tour, as we're standing inside a gaudy, gold-encrusted church, we decide to test Petr's flexibility by announcing that anything baroque tends to prompt our gag reflex. That'll knock quite a few stops off the standard Prague architectural roundup, and he looks discomfited, hurt even. But he quickly rebounds, taking us next to a rare example of cubist architecture, then deep inside the Municipal House, a dazzling art nouveau structure, followed by the Zivnostensk Banka, an off-the-beaten-track bank with a spectacular stained-glass ceiling. At dusk we challenge him to take us really off-grid. As he leads us down deserted cobblestone lanes below Prague Castle, bounded by crumbling stone walls on one side and big, studded medieval doorways on the other, we enjoy a reverie not possible with 40 other tourists in tow.

On day two it's flexibility from the first, when Joeri cannily begins our tour at a 3-D model of the city, where we enjoy a bird's-eye view of different neighborhoods while bantering about ideas for the day's itinerary. Quaint, hidden alleyways? Yes, please! National Theatre? Pass. Art nouveau district? Absolutely. Then we'll finish at the bucolic Vysehrad Park with its historic cemetery.

To a large degree we judge a private guide the same way we would a group guide: on how well he knows his stuff and how vivid he makes the most memorable details. Joeri, a cheerful, fresh-faced thirtysomething, offers the clearest, most complete explanation we've heard of the city's famous astronomical clock. He explains that those over-the-doorway plaques we keep seeing the white unicorn, the three violins are actually original Renaissance house signs. And he delights us with pungent oddities: a bronze sculpture of Sigmund Freud dangling by one arm over the street, a gnome hiding high on the facade of a stately apartment building.

But even the most engaging guide can cram only so much information into our cranium. We find ourselves standing alone with Joeri in Old Town Square, eyes locked, head nodding, as he tries valiantly to pack hundreds of years of Prague history into a dizzying 15-minute brain dump. With no chance to fade to the back of the group, overload quickly sets in. As our nods become more obviously robotic, Joeri moves quickly to the topic of defenestration. Our ears perk up as we scan nearby palaces. Which window, exactly, did that Hapsburg guy get tossed from?

Turns out the private-guide relationship is a fairly intense and intimate thing with our only downtime coming during trips to the restroom. Between sights, our various guides give us earfuls about their real estate woes and grandchildren's weekend ski plans. With our most reserved guide, lunchtime features more than a few awkward silences. But many private-tour takers say that getting to know a local is the best part of the experience. And in fact our guides tell profoundly moving stories about life under communism. Petr had defected in 1981, using his life savings to bribe his way out. As we stand among the tourists outside Prague Cathedral, he shares his harrowing recollection of Aug. 21, 1968, the day Soviet tanks rolled into Prague. "See those bullet holes?" he asks, pointing at a derelict palace. "I hid behind that sculpture while the tanks fired off warning shots. I was 17 years old." After days of looking at old buildings, we feel our most compelling connection yet to the ongoing history of this fascinating city.