You can find garages of the standard car, bike and tool-storing variety all across America. But perhaps only in Silicon Valley, that nebulous area cradling the southern half of the San Francisco Bay, have they become tourist destinations.

Within a 14-mile swath near Stanford University there are three mystique-surrounded and era-defining properties that served as incubators for some of the most influential tech companies of our time: Hewlett-Packard, Apple and Google. None of the garages are open to the public, but that hasn’t stopped them from becoming go-to spots on geek tours, luring pilgrims to otherwise calm neighborhoods, some of them perhaps hopeful they might one day start a company of their own that will change the world, or at least make a ton of money.

The HP Garage (at 367 Addison Avenue) in Palo Alto — a wood-frame, pitched-roof 12-by-18-foot building where William Hewlett and David Packard tinkered in 1938 and 1939 — is the granddaddy of the bunch, the “Birthplace of Silicon Valley,” according to a bronze sign out front. Not only an official Palo Alto landmark, but also a California landmark and listed on the National Register of Historic Places, it is owned by Hewlett-Packard, which has painstakingly restored its 1930s look, complete with workbench and Craftsman drill press. It opens the place only occasionally for business meetings, however, leaving tourists to peek through an iron-barred gate from the sidewalk.

Apple has no official relationship with the garage in Los Altos (2066 Crist Drive) where Steve Jobs and Steve Wozniak started their computer company in 1976. Meanwhile, Google’s ranch-house garage in Menlo Park (232 Santa Margarita Avenue), which its founders Larry Page and Sergey Brin rented in 1998 and 1999 after conceiving their search-engine enterprise in a Stanford dorm room, was purchased by the company in 2006, though it hasn’t quite figured out what to do with the place. “The idea was simply to hang on to bit of tech history,” wrote a Google spokeswoman in an e-mail message.

So ingrained in the culture of Silicon Valley is the idea of the garage as lab — a place not to house something but to hatch something — that local companies have taken to using the word “garage” in their names, and the Avatar, a hotel that opened last year in Santa Clara (408-235-8900; jdvhotels.com), has an executive conference room called the Garage — outfitted with supplies stored in a red rolling tool chest.

— JANE MARGOLIES