To the first-time visitor, London seems to sprawl to the very edge of the planet. Yet few big cities are so easily escaped. Get on a train, ride for less than an hour and you can step down into countryside as fresh and green as in any fairy tale. The city will seem a thousand miles away.

The Darent Valley in Kent is such a place. It's got sheep and chalky footpaths, fields of hop and a river that winds gently toward the Thames. Inhabited since before Roman times, it also has plenty that reflects a diverse past: stone bridges, castle ruins and villages where you might share a lane with a horse and rider.

What follows is a guide to a country walk for the London-weary traveler. It's just one of many such excursions that are there for the taking--around their capital, the English have managed to preserve pockets of green where development is controlled and a taste of the old life remains.

You can find guidebooks for walkers in many London bookstores. If it's the Darent walk you choose, it's best to go during the week. London has armies of weekend hikers, and the valley isn't exactly undiscovered. Bring some drinking water. You can buy lunch in many of the village pubs you'll pass. Total distance on foot will be about five miles, though there's a place where you can break off midway if you've had enough. At a leisurely pace, taking time to stop and browse, I found it a full-day's excursion.

Start off by getting yourself to Victoria or Blackfriars station in London reasonably early in the day and buy a round-trip ticket to what's going to be the end point of your walk, the village of Otford. Off-peak, it costs about $9.75; peak is about $13. It's best to buy the more costly ticket to give yourself the flexibility to return at whatever hour you want.

But board a train for Eynsford, where you'll start your hike. Out the window, south London will fall away. One moment, you'll be passing tiled houses with tiny walled gardens out back; the next, you'll be in farm country.

Step out of Eynsford station and turn left to head along the road down the hill. You're walking into a village that as long ago as 1086 was big enough to have two churches and two mills--this from the Domesday Book, the famous toting-up of booty that William the Conqueror ordered after overseeing the Norman conquest of England. Home today to about 2,000 people, Eynsford has adapted to the 20th century but scrupulously maintains bygone airs.

You'll soon come to St. Martin's, a stone church that dates in part from the Norman era. English villagers over the ages have taken pride in adding to their churches--my favorite addition to this one is the 15th-century wooden spire that pokes high above the village and announces the church's presence for miles around.

Take a walk up some of the little side lanes along the main street. You'll find beautiful old homes, some of which bear the kinds of names the country English love--Willow Cottage, Rose Cottage. Flower beds are scrupulously maintained, of course.

A few hundred yards past the church, follow the sign saying Village Hall to find the ruins of a castle, which dates to Norman times as well. Some of the flint walls still stand 20 feet high. Wander around and you can make out the remains of the moat (now dry), a thick-walled house and other things that a Norman lord and family would need for comfort and security from potentially hostile locals. Other former residents of this picturesque spot: foxhounds, which were kenneled in the ruins into the 19th century, before the English got preservation-minded.

From the castle you'll look onto a pasture and the River Darent, which despite the grand name isn't much more than a stream.

Eynsford is more than pretty sights, though. It has a long history as a refuge for creative talent. For instance, a 17-year resident here was the English songwriter Ross Parker, coauthor of a patriotic number much heard during World War II, "There'll Always Be an England." Some of its sentimental lines fit the Darent Valley nicely:

There'll always be an England

While there's a country lane

Wherever there's a cottage small

Beside a field of grain.

And today the cultural life continues. "We have gardening clubs, an . . . amateur dramatic group," says Margaret Hilling, who holds the post of parish clerk in the village. "We have a very active village society."

You may notice some expensive cars as you walk around. Though the village looks all country, it's in part a costly bedroom community for London. Many of the cottages have been bought up by lawyers and bankers--you'll see them in force at the train station if you're there at commuting time.

You may also see some of the old-time villagers making day trips into London. "We get the best of both worlds down here," says valley resident Caroline Alexander. She manages a nationally known dried-flower store here called the Hop Shop, but she gets to London often enough that her establishment has won five gold medals at the annual Chelsea Flower Show.

Back toward the village center, you can cross the Darent on a 17th-century stone bridge. Next to it you'll see the ford of the Eynsford name. Splashing noisily across, trucks still use it, so as to avoid damaging the bridge, which local tradition says once did duty as an outdoor pulpit for John Wesley, a founder of the Methodist movement.

As you head out of the village, you'll see a large house in the "half-timbered" style, from the Tudor period, the time of Shakespeare. It's now a pub called the Plough. You can stop for a drink or meal here, though there will be others ahead.

Street names here can be as nice on the ear as those of the cottages. On the right you'll pass Sparepenny Lane, called that because using it allowed people to bypass a toll collector on the main road. Keep going and you'll pass under a railroad viaduct and move along more pastures. Watch for wildlife--I spotted a gray heron when I did the walk in April.

In about half a mile, you'll come to the remains of a Roman villa. The Romans ruled England for close to 400 years, and along the valley they built villas that functioned much like plantation houses of the American South, overseeing farm production. This one went up on a gentle hillside overlooking the Darent sometime around A.D. 100. It's mainly foundations and floors that remain, but they've been painstakingly excavated and you can get a good feel for the place. For instance, you can see down into rooms that had the steam baths that rich Romans loved. Large, colorful mosaic floors survive, including one that shows Jupiter, in the form of a bull, abducting Europa. You can see a touching memento of daily existence: a clay roof tile bearing the single paw print of a dog.

From the villa, walk along to Lullingstone Castle. Though the road is marked as "private," it's fine to use it--an official walking route for the valley runs along the road. You'll pass more pastures, then come to the castle, which is a large country estate built in many styles over many centuries. The tall brick gatehouse with twin towers is from the Tudor period; Henry VIII, the story goes, stopped over during a trip down the valley.

The castle is not a place that changes hands often--the Hart Dike family that lives there today is descended from a man who acquired the property in the 14th century. Historical footnote for lawn tennis fans: In Victorian times, Sir William Hart Dike and several friends played the game frequently on the castle grounds; together they worked out formal rules that were adopted in 1875.

You'll soon pass through a nature preserve. Keep an eye out for mallard ducks and the blue feathers of kingfishers. To the right, if you choose, you can go up the hillside and explore some nature trails in an area that was set off as a deer park during the reign of Queen Elizabeth I.

You'll come to a bridge and road. Take the road in the direction you've been traveling. You'll come to Caroline Alexander's Hop Shop on the left. Past it, where a sign marks the footpath, strike out across rocky fields where the shop's flowers are grown.

The next village of your journey, Shoreham, is a postcard place of little stone houses and winding streets that seem too narrow for cars. Situated off the main road, Shoreham is quieter and more slow-paced than Eynsford, with fewer commuting residents. It's the sort of place where you might see a horse and rider on its main street. There's a famous music festival here in the summer. On the more whimsical side, people gather in May at the Darent with artificial ducks made of whatever they can find--cans and plastic bottles, perhaps--and race their creations on the water.

"It's like a lost world, this village--it's lost in time," says Mack Bermingham, who runs a local courier business and stopped by Shoreham's Ye Olde George Inne for a pint one recent afternoon. The pub has that standard country feel--a bit dim inside in terms of light, but bright in cheer and welcome.

There's another Norman-era church here, the Parish Church of St. Peter and St. Paul, built of brick and flint. Take some time to walk in its graveyard and read the headstone inscriptions--it will give you an idea of who the big families were in different periods of the community's history. The yard is the resting place of two brothers, Richard and Cecil Cheeseman, who died five days apart in August 1917, victims of World War I; you can still find Cheesemans in the village.

If you're tired now--you're about two thirds of the way--you can head up the hill to the Shoreham train station and return to London. Otherwise, you can continue on the footpath to Otford, another mile or so ahead. The trail will become chalky (you're not that far from those white cliffs of Dover). It will lead you down a longish hill, with fields on either side, and Otford coming into view ahead. Perhaps you'll catch the scent of burning firewood. In Otford, you'll find more places for food and exploration. If you're historically inclined, scout the ruins of a brick palace that Henry VIII seized from the Archbishop of Canterbury.

These days it's gone to seed, and that's part of the charm. Locals walk past it and pay little attention. But gaze up at the twinned windows of its tower and you might be able to imagine the portly Henry surveying his realm. The place is small now (this is its only remaining tower), but an indication of its former size comes from a 1573 survey that indicated that 200 door keys were missing.

When you've had your fill of the country, head up the hill and catch the train to London. Back in the city, you'll feel the bustle, smell the cooking fries, hear the chatter of passing teenagers. And you'll shake your head and wonder if it really is possible that just an hour earlier you were out there.

You were. Count it as another trait of London that will keep you coming back.

John Burgess is an editor for The Post's Business section.