GATEWAY TO AN endless tunnel that triggers nightmares of car failure within, rows of white marble steps, a huge clock tower with Bromo Seltzer lettered in for the numbers. A place to turn left away from at the BWI airport, and avoid on the way down from New York.

A getaway to Baltimore?

But wait. Things have been happening to our neighbor over there. The city has had a cultural renaissance that is changing the character of this traffic-choked old city, once content to rest on its historical past. Something new has been added to the city of Mencken, Babe Ruth, Dos Passos, Eubie Blake and Wallis Warfield.

No matter what else you intend to see in our eighth largest city, you should take a look at this harbor. The showpiece is the World Trade Center designed by I. M. Pei, rising 27 stories above the harbor and offering an unparalleled view. There's also a new science center with a planetarium and living science programs, and on July 2 Harborplace, the complex of 125 shops and restaurants being built by James Rouse, will be open. Next year the new aquarium rising from Pier 3 will be opening its displays of 600 species of water-oriented creatures as well as recreations of a Maine cove, an Atlantic coral reef and a tropical rain forest.

Then, of course, there's nearby Hopkins Plaza, well lighted and policed so that foot traffic has returned once more to the center of town. The Hilton is undergoing a $5-million renovation and a new $5-million convention center is already in use. Everything's up to date in downtown Baltimore, including the attitude toward ethnic neighborhoods, now metamorphosed from an embarrassment to a center of old-world charm. Little Italy, lying so close to the harbor, is a newly discovered tourist attraction with its narrow streets and its myriad shops offering homemade pasta and Italian sausage.

Much of the Inner Harbor remains to be finished, but it's well worth the trip to visit the Top of the World in the Trade Center. At your feet lies Baltimore harbor, where 4,400 freighters call each year, and if you have wondered how it feels to sail on one of those feighters, you can stand on a simulated freighter deck by the window and dream. You can even try your hand at operating a cab crane, courtesy of some levers that appear to control the loading of a ship on a small screen.

Coffee beans and myriad other import and export products are piled high against one wall in the trade center to remind you of how the harbor ties the city to the world. A small gift shop offers wares from ports the freighters touch, and a make-believe park with old street lights and benches attracts the weary. The children can watch a slide show designed to given them the flavor of the city, and a "mutascope" offers rapidly flickering pictures of an early Baltimore parade. (They say the reverse of these pictures shows a nude lady, but the public will never see them.) You can, however, view an umbrella enshrined in a frame to remind visitors that the first umbrella invented was raised to keep the rain off the head of a Baltimorean.

Down below, in the harbor, the USS Torsk, the submarine that sank the last two ships of World War II, awaits visitors; and until May 20, the Pride of Baltimore, a reproduction of an 1800's clipper ship, will be open for inspection. The Constellation is in dry dock.

So much for renovated downtown Baltimore. And then there's that other Baltimore, where things will always be the same. Downtown Baltimore may be changing its face, but beyond the beltway in horsey exurbia lies another world untouched by time. Out here the freighters and the city itself are a distant rumor, and the shining glass and steel of the new Baltimore fades like a dream in the rolling countryside.

For an antidote to the busy harbor, take the Towson exit from 695 and drive 14 miles north into Harford County to the topiary gardens of Harvey S. Ladew. Make it a Sunday, 12 to 5 p.m. (or a Wednesday, 10 to 4 p.m.) because on these days his house is also open, an old-fashioned farmhouse that knows nothing of urban face-lifting.

The horse is king, as it has always been, out in the green world. Sleek trotters and race horses graze beyond the fences all the way along the two-lane road to the Ladew farm. This is the land of the fox hunt, and turning into the Ladew gates the first thing you see are the horses and dogs in full cry. The odd thing is, they are all fashioned from yew.

Ladew's marvelous topiary, imaginative shapes sculpted from greenery, is better known to English horticulturists than to many in the Baltimore-Washington area. He fell in love with topiary on his visits to England, and when he decided to leave his native Long Island for Harford County -- where there were no wire fences to make fox hunting difficult -- he designed his own gardens.

His old farmhouse, decorated by Billy Baldwin, is stuffed with the treasures of a lifetime, but none was dearer to him than the medal in the Garden Clubs of America gave him for the most outstanding topiary garden in the country developed without professional help.

The topiary creatures were formed by training the living plant into a wire frame and clipping recalcitrant branches. A reindeer complete with antlers watches the front door, a lyre bird spreads his tail in the sculpture garden beside a unicorn, sea horses and replica of Churchill's top hat.

There is even a topiary Henry Moore sculpture, the only abstract in the lot. Close by the house lie the terrance gardens, which stretch over three levels and are designed to look like outdoor living rooms. The hemlock walls are clipped into garlands and pyramids, adorned with French hens sitting on nests and cut through with windows to open the view.

Ladew has been dead since 1976, but his sense of fun still comes through to guests in his house. In the apple orchard, he tucked away a statue of Eve offering Adam the apple. Around the sundial he had carved the words of Hilaire Belloc: "I am a sundial and I make a botch/Of what is done far better by a watch." The view from an open window in the tea house, once the ticket booth at the London Tivoli theater, is framed like a landscape painting. Above the doghouse by the front door of the farm is painted an unattributed poem, maybe his own: I love this little house because It offers after dark A pause for rest, a rest for paws, A place to moor my bark. Ladew never married and the house, which like the gardens is listed on the Register of Historic Places, was left to a nonprofit organization. Among the treasures are more absurdities to prove he wasn't one to knuckle under to the expected. His bedroom is perfection -- an old four-poster, his hunting pinks laid out complete with needlepoint slippers featuring fox heads, a French history on the reading table . . . and beside the bed an ashtray inscribed, "God bless this lousy apartment."

His portrait as mater of the Elkridge-Harford Hunt hangs in the hall, and it is easy to imagine the hearts he must have fluttered with his dark good looks and his huge inherited fortune. He spent most of his time traveling in search of adventure, making friends amid the famous of his day.

Once he accompanied a naturalist on an expedition to a South American mountain range where a new breed of mouse was named after him. Crossing the Arabian desert he felt the wind and, bedding down with a caravan of Bedouins, wrapped himself in the dinner jacket his uncle had cautioned him to bring. He was a close friend of Edward VIII, before and after his abdication, and of Lawrence of Arabia. "Everything, everywhere is changing," laments a letter written in 1924 by Lawrence and preserved on the wall.

Ladew lived with imagination and verve. He bought a particularly fine oval desk in England and, finding no room big enough for it, built an oval room to accommodate it. The room is said to be one of the 100 most beautiful rooms in America and is lined with 3,000 volumes of first editions and biography -- with a bit of classic erotica thrown in. He had a secret panel added so that the wall swung wide to allow him to disappear into the card room. When he tired of tennis and took up croquet, he brought a part of the net indoors and had it attached to a Sheraton hunt table to catch the empty bottles at the hunt breakfasts.

Even children love Pleasant Valley Farm, making a game of discovering the hunt motif hidden everywhere. They love the mantle clock that plays a march, a minuet and a sonata, and the trompe l'oeil painting done by Ladew himself for the dressing room his sister Grace used when she visited. The painting takes an entire wall, turning it into a chest of drawers from which dangle bits of intimate feminine wear; two chairs at each end are also awash with discarded bits of lingerie.

Don't miss the silver dollar embedded in the newel post to signal a paid-up mortgage in 1847, when the former owner lived here. Or the thank-you note from the prince of Wales after a loan of Ladew's favorite mount, The Ghost. The purple finches' houses in the garden are as elegantly designed as any summer cottage.

Bucking the inflationary trend today, the admission charge here is actually less than last year. Entrance to both house and garden now costs $3.50 for adults, $2 for students and seniors, $1 for children.

If you get hungry being a Ladew voyeur, one of Baltimore's best suburban eateries is the French Bread Factory, a restaurant in Cross Keys Mall. It's on the way back to Washington and a top-rated spot for homemade soups and the house specialty, jambon croissant made on the premises and wrapped around southern ham. The selection of patisserie is wicked temptation. Take the Baltimore Beltway to 80 south, four or five miles to the Northern Parkway exit and turn left on Falls Road to Cross Keys, an early percursor of Reston and Columbia. The Factory is in the side of the mall.

N.B. If you are a night owl, you can join the insomniac's tour and see Baltimore's life at night. It begins at 1:30 a.m. and ends at dawn, taking in everything from Edgar Allan Poe's tomb to the pre-dawn workout at Pimlico. Call Baltimore Rent-a-Tour, 301-653-3998. $20.