Kansas City, Mo. — From the outside it looks like any of those deep dark Missouri caves author Mark Twain used to describe.
But once you drive in, you find a veritable ''subterropolis'' of paved streets (complete with stop signs, speed limits, and fluorescent lighting), dozens of giant trucks parked at loading docks, and a number of plush offices equipped with thick carpeting, wood paneling, and plenty of glass.
It's Kansas City's underground answer to the downtown space crunch and those skyrocketing energy bills.
Actually this part of northwest Missouri, ideally situated as a storage and transit center in the nation's midsection, has been using its laterally cut, close-in limestone mines for storage and manufacturing purposes for some time. (The so-called ''room and pillar'' method long used in mining here creates vast underground spaces that are ideal for storage.)
But the pace of acceptance of this unusual idea has markedly improved in the last few years as energy costs have soared.
''I wouldn't say people are just taking to underground space (in a rush) - it does have limitations and there's still a psychological barrier there - but I do see it growing continuously as long as there's an energy shortage,'' says Dr. Truman Stauffer Sr., a professor of geosciences and director of the Center for Underground Space Studies at the University of Missouri.
The cave described above, located at 8300 Underground Drive, happens to be owned by the Great Midwest Corporation, a land development company headed by enterpreneur Lamar Hunt. It is the largest of the more than a dozen underground limestone sites being used for more than strictly mining purposes in the Kansas City area.
Its 100 tenants are using only about one-fourth of the potential space available. Great Midwest president Forrest Browne says his company holds enough reserves below ground to keep expanding at an annual rate of 25 acres for the next 30 years.
Chief use of space here, as in most underground developments, is for storage and warehousing. In the foreign-trade zone, where import duties need not be paid until the goods actually leave the premises, you'll see stacks of everything from red pottery mugs and wallpaper made in West Germany to cans of Pacific Ocean crabmeat waiting to be labeled. A guard checks our trunk as we leave the zone to be sure the warehouse area is no poorer for our visit.
Further on one sees the comfortable-looking offices of a computer firm, a company that will begin assembling TV sets from imported parts, a toy company loading swimming pools onto a truck.
Though small manufacturing generally accounts for less than 10 percent of the use of underground space, employee productivity, without the distractions of windows and weather-watching, is said to be high. Officials of K. C. Envelope, for instance, which rents space from Great Midwest, say their envelope production has tripled since the company moved underground in 1969.
Great Midwest's latest coup is the decision by the US Postal Service to move its collector-stamp and order-filling divisions from the scattered surface in Washington to the consolidated underground space of Kansas City in July. The Postal Service has said it expects to save $250,000 a year by the move just in heating and cooling costs.
Certainly the easily expandable space and the constant year-round temperature in the mines of 59 or 60 (warmed a good 10 degrees by the presence of people and traffic), requiring no heating or air conditioning, are key advantages for those thinking of moving underground. The only climate-control expense is a relatively modest one for circulating and dehumidifying the air.
While some employees might complain of a closed-in feeling with mottled whitewashed limestone ceilings and pillars on every side, those people usually don't apply for jobs here in the first place. Most workers say there is a comfortable spacious feeling that the extensive use of glass in walls and doors affords. They say they rarely miss a window to the outside world.
''We do often ask people what the weather is, but sometimes you're better off not knowing,'' says Rose White, a secretary with Great Midwest. ''And the parking is out of this world - you never have any ice or snow to scrape off.''
Mr. Browne suggests that such employee enthusiasm is closely related to being part of something ''new and exciting.''
Though Mr. Browne can visualize the day when a restaurant, beauty and barber shop, and a bank will be part of his underground complex, he shares the view of most underground space experts, that the concept's potential for office use is strictly limited. Moreover, he concedes it is not for every commercial or industrial enterprise. For instance, anyone relying on the use of natural gas, which would be dangerous in this environment in the event of a leak, or requiring a very high ceiling, should not even consider an underground move.
''But we figure these constraints would affect only 15 to 20 percent of US industry, and we're aggressively going after everybody else,'' says Midwest's president, who admits he puts a premium on aesthetics from carpeting to careful painting of the limestone walls and pillars. He is also about to invest $600,000 in planting grass and flowers on the bluff overhead.
One major obstacle for many underground developments has been the scepticism of bankers and others who would not make the loans to put up the money or even take a look at the property. Great Midwest was able to leap that hurdle a few years ago when it persuaded a major New York life insurance firm to make several million dollars available for loans.
For Kansas City, the future for underground development looks bright.
''The use of underground space is definitely increasing,'' insists Warren Lewis, president of Inland Storage Distribution Center, the second largest underground development in the area and one which has set aside the great majority of its space as a refrigerated warehouse for perishable foods. Like his Great Midwest counterpart, Mr. Lewis estimates that his firm can keep on mining and expanding in the territory it now owns for at least another 30 years.