As 2000 approaches, clock consciousness is taking hold: This Friday, millions of people will ponder the world's most ubiquitous machine. But for the clocks that started it all, some 700 years ago, the turn of the millennium will be just another day.

In Salisbury, England, the wood-and-iron clock in Salisbury Cathedral proudly ticks away the hours, as it has since the 14th century. Thirty-five miles west, the timepiece in Wells Cathedral has the world's oldest surviving clock face. Each machine is housed in a charming city in England's West Country that, taken together, make an easy day trip from London. Between Wells and Salisbury lie the rolling hills of the Salisbury plain, as well as the ancient stone circles of Avebury and Stonehenge.

But first, check out the clocks. The Salisbury machine, in the cathedral's north transept, hardly looks like a clock: The wheels and gears are mounted in an open, cube-shape iron frame, about four feet on a side. It has no face or hands; it told the time only by striking the hours. Incredibly, there are no nuts and bolts (they had not yet been invented); the parts are held together by dowels and pegs.

How does it work? Two large weights drive the clockwork; as they fall, a rope unwinds from a wooden barrel, turning a large geared wheel. Its motion is controlled by an "escapement"--perhaps the greatest of medieval inventions--in which a long iron bar swings back and forth, alternately stopping and releasing the main wheel. Thanks to the escapement, the clock ticks away at a precise, controllable rate.

The clock's origins are unknown, but the cathedral's records show that a man was paid to wind it as early as 1386. "How long it was here before that, we can't say," says John Plaister, the cathedral's current clockkeeper. "But I've no fear to say it's the oldest working clock in England."

Like Salisbury, the city of Wells --half an hour's drive west--owes its living to its magnificent cathedral. In fact, the cathedral, together with the massive bishop's palace immediately to the south, make up nearly the whole city--save for a few crooked streets lined with half-timbered houses and a handful of pubs and shops.

The Wells clock may have been built by the same man who made Salisbury's--records show that it was there in 1390. But this timepiece has a magnificent face, with elaborate paintings of the earth, moon, sun and stars--a colorful, 14th-century model of the known cosmos. It's probably the oldest surviving clock face in the world.

The large outer dial shows roman numerals from 1 to 12 twice over, making a 24-hour display. A smaller circle within it shows the minutes; another displays the day of the lunar month, while an ingenious graphic shows the phase of the moon. (The lunar cycle was critical for determining the date of Easter and other feast days.)

For a glimpse of the medieval sense of humor, look above the dial, where a 3-D display of four wooden knights on horseback goes around in a circle every quarter-hour. As the warriors spin around, one of the knights always knocks his opponent flat on his back, only to be propped up again seconds later. Someone has calculated that he's been knocked over some 53 million times since the clock was built. "To me, it's a great lesson in perseverance," jokes the Rev. Norman Lemprere, a volunteer at the cathedral. "Everybody else thinks he's thick--he should have learned to duck by now."

Salisbury is about 180 miles southwest of London. Take the M3 west to Bastinstoke, then head west on the A303 and follow the signs. Trains serve Salibury from London's Waterloo Station; the trip takes 90 minutes and costs about $34 round trip. A donation of $5 is requested at Salisbury Cathedral (www.salisburycathe- dral.org.uk).

Wells is about a half-hour's drive west of Salisbury. Or take the train from London's Paddington Station to Bath (75 minutes, $52 round trip); from Bath, catch Bus 173 to Wells (about $8 round trip). Wells Cathedral (http://home.clara.co.uk /r.l.collins) requests a donation of $6.

For more information: British Tourist Authority, 1-800-462-2748, www.visitbritain.com.