Editor's note: This tour of small businesses across the country highlights the imagination, diversity, and resilience of American enterprise.

The hilly seaside community of La Jolla, California, just outside of San Diego, is a glorious blend of artifice and nature. Streets lined with upscale boutiques, galleries, and restaurants overlook pale, pristine beaches, nestled between cliffs and lapped by the Pacific. No place better captures that dynamic than the Cave Store. On top, it is a conventional beachside shop with gifts, jewelry, and women's clothes; below, a shadowy cavern loud with rushing water. Just try not picturing pirates.

The passage between cave and land was created back in 1902, when a German mining engineer named Gustav Shultz enlisted the help of two Chinese workers to bore a tunnel through the rock. Recognizing the commercial opportunities, Schultz started charging people a few cents to be lowered into the cave with a rope, according to the travel site Atlas Obscura. Ever since then, it has been a tourist destination. Visiting Wizard of Oz author L. Frank Baum came up with the colorful name Sunny Jim's Sea Cave after noting the resemblance of the cave's mouth to the profile of a 1920s cartoon character. 

"Everybody knows about it," says Jim Allen, the Cave Store's current owner. "It's one of the very oldest businesses in La Jolla. And it's the only underwater cave in California that you can get to by land."

To access it you must first walk in the Cave Store's sunny entrance. Go straight through and you are in Lulumars, a separate shop selling jewelry, clothing, and gifts. Or turn to the right and (after handing over $6, or $3 for children) you can descend 145 narrow, faintly lit stairs surrounded by damp, sandstone walls. Standing in darkness on the wooden platform below, you gaze out through Sunny Jim's ragged profile at swimmers, snorkelers, and kayakers at play in the sparkling Pacific.

"It's confusing...and interesting until you get into the cave itself, and think, 'Oh my gosh, this is wonderful,'" Allen says. 

Here come the tourists.

Allen, who originally hails from Michigan, moved to San Diego in 1965. He bought the Cave Store in 1994. Up until then, the business chiefly made money selling seashells. Today, Allen estimates that 90 percent of revenues come from entrance fees to the cave. The shop brings in $30,000 annually in merchandise sales and "hundreds of thousands of dollars" in ticket sales. He has kept the business intimate, with just three employees. 

"In the years I've been here I've been getting customers from all over the world," says Allen. Most of the Cave Store's business, not surprisingly, is tourism--around 60,000 visitors annually, with the majority arriving in summer. Allen doesn't have to advertise. The business is so distinctive it attracts write-ups and reviews from sites such as TripAdvisor.

Allen also rents snorkeling gear, charging $20 for two hours for a snorkel, mask, and fins (which translates into roughly $50,000 annually). La Jolla Cove, where the shop resides, is ideal for that activity: warm water, gentle waves, a rainbow's worth of fish, and occasional visits from seals and sea lions.

There are other, non-nature-related advantages to doing business here. Early on Allen was able to get the cave designated an historic landmark by the city, which has proved useful for business. He pays lower property taxes and is not required to have bathroom facilities. He also claims he need not comply with the Americans with Disabilities Act (ADA), since the cave cannot be altered or enlarged to accommodate wheelchairs, for instance. Nor has Allen had to pay increased insurance rates for safety or property upkeep, other than the cost of replacing the railing and some steps a few years back. 

The smell problem.

For all of its natural beauty and commercial appeal, La Jolla can be "a dysfunctional place" according to Allen. By way of example, he cites a 2013 incident in which local merchants sued the City of San Diego and the State of California over a pervasive odor in the neighborhood of La Jolla Cove, caused by a buildup of bird and seal excrement. (The group lost.) 

Allen ran into trouble when he tried to address the smell problem by planting a couple of trees and some other vegetation on a bluff near the store. The idea was to impede erosion, but he also hoped the scrub would deter seabirds from fouling the area. However, his use of public land without a permit stirred resentment among some locals. Allen's take is blunt: "The city seems to be very confused on the issue. They don't know what to do."

Most locals, however, are happy to have Sunny Jim's around. Jennifer Luce, founder of the architecture firm Luce et Studio, calls the Cave Store "an affectionate and powerful presence" for the community--one of the "final remaining historic businesses" in La Jolla. Certainly restaurants and retail concepts come and go. But a 200,000-year-old sea cave is pretty much forever.