(MONEY Magazine) – Quick quiz: what's the best-known work of art in America? Here's a hint: It's not in a museum, it's nowhere near any of the major metropolitan art scenes, and it's a prime travel destination.

The answer is Mount Rushmore, which is obvious once you stop and think about it. The reason you may have to think about it, of course, is that very few of us conceive of Mount Rushmore as artwork. Part of this is due to Rushmore's entrenched status as a national memorial, but I think it's also because many of us have accepted the notion that art exists only in museums and galleries. But that's not the case, and nothing demonstrates this better than roadside art, which can be found all over America and makes for a great stop on any trip. The massive Rushmore is admittedly an extreme example, but there are a lot of more down-to-earth roadside specimens situated along our nation's highways, waiting to be stumbled upon while you're heading from here to there.

Roadside art often isn't as polished as museum pieces, but it's nonetheless brimming with the inspiration and revelation that have always informed the best artwork. And in a nice twist, roadside art is frequently made by people who didn't even consider themselves artists until they began their projects. A great example is Carhenge (U.S. Highway 385, just north of Alliance, Neb.; 308-762-1520; free), a spectacular Stonehenge-patterned auto sculpture that I encountered a few years ago while driving through the barren Nebraska flatlands (see "Right out in the Open," November 1998). It was built in the mid-1980s after a fellow named Jim Reinder got the idea during a family reunion. Initially ridiculed, Carhenge is now an acknowledged American treasure.

Here are some of the other wonderful roadside art sites I have visited over the years. All of them qualify as destinations in their own right, but you may prefer to make them a detour on a longer trip; the box below has information on which sites are near major driving routes to more conventional destinations. Some are free of charge, but go ahead and leave a donation--you'll be helping to defray the costs of upkeep and maintenance, and you'll get to feel like a genuine patron of the arts.

Cadillac Ranch (I-40, about six miles west of Amarillo, Texas; 806-374-1497; www.texasmonthly.com/archive/cadillac.html; free). Another fantastic car sculpture, this one consisting of 10 vintage Cadillacs half-buried nose-down in the ground, their protruding tail fins documenting the Caddy's design evolution from 1949 through 1964. Created in 1974 by a San Francisco art collective called the Ant Farm and situated in a wheatfield owned by the eccentric Amarillo helium magnate Stanley Marsh III, Cadillac Ranch is a playful tribute to the open road. It's also the most interactive artwork on this list--visitors can wedge themselves into the cars, climb on them, even spray paint them. About the only thing you can't do is steal the wheels and hubcaps, which have all been welded in place.

Wisconsin Concrete Park (Route 13, Phillips, Wis.; 800-269-4505; outsider.art.org/fred; free). Fred Smith, a retired logger with no art training, didn't plan on becoming a sculptor at the age of 62--it just sort of poured out of him. Working primarily in concrete decorated with colorful pieces of broken glass and mirrors, he made more than 200 large, festive sculptures between 1948 and 1964, most of them depicting animals, scenes of small-town life and American icons like Paul Bunyan, Sacagawea, Abe Lincoln and the Statue of Liberty. His work has a wonderfully childlike sense of accidental genius, much like the more celebrated folk art of Howard Finster (who has his own roadside sculpture park, Paradise Gardens, Summerville, Ga.; 800-346-7837; www.finster.com). Smith died in 1976, but placards with some of his more illuminating quotes--including his mantra, "It's gotta be in ya to do it!"--are scattered around the small park where his work is now displayed. The site is maintained by Price County, making it one of America's most inspired examples of publicly administered art.

Grotto of the Redemption (300 N. Broadway, West Bend, Iowa; 515-887-2371; www.nw-cybermall.com/grotto.htm; $5). Grottoes are among the most stunning roadside artworks. There are several beautiful examples, but the biggest and best is clearly the magnificent Grotto of the Redemption. The sprawling, rocky shrine, with its winding stairways, balconies, statues and mosaics, is studded with countless crystals and gemstones (its estimated geological value is over $2.5 million), creating the sense of a huge, glittering sand castle--truly a place that has to be seen to be believed. It's also an obsessive labor of love: The project, which has never had a blueprint, was launched in 1912 by Paul Dobberstein, a Catholic priest who worked on it tirelessly--often hauling gems from hundreds of miles away--until his death in 1954, after which his assistant continued the work into the 1990s. Today the Grotto, still managed by Dobberstein's diocese, is a popular destination for religious and secular travelers alike, with guided tours available.

Tinkertown (Route 536, Sandia Park, N.M.; 505-281-5233; www.tinkertown.com; $3). Essentially a folk art collection inside a gigantic folk art sculpture, Tinkertown is an utterly charming and seemingly endless assortment of homemade figurines and dioramas, many of them mechanized, depicting scenes of circuses and the Old West, plus lots of little mini-sculptures just about everywhere you look. The overall effect is like a penny arcade mixed with a carnival, and the whole thing is housed in a bizarre structure made in part from old glass bottles and bicycle wheels. Tinkertown's incredible torrent of good cheer flows from Ross and Clara Ward, who've been working on the facility for more than 40 years and whose motto aptly sums up the spirit of roadside art: "We did all this while you were watching TV!"

For more information about most of these sites and hundreds of others, read A Guide to the Sculpture Parks and Gardens of America by Jane McCarthy and Laurily K. Epstein, which makes a valuable addition to any travel library.

Award-winning travel writer Paul Lukas may not know much about art, but he knows what he likes.