The Illinois and Michigan Canal path is not a secret. It's probably just the best local running trail that almost no one thinks of running on.

It used to be the mule track on the bank of the Illinois and Michigan Canal: the towpath on which mules once hauled canal boats 97 miles between Bridgeport and LaSalle. It now is the western 55 miles of the old towpath reclaimed during the past 25 years; it runs from 1-55 to LaSalle, and in a couple of years it should be reclaimed for six more miles, north and east to the outskirts of Joliet.

The canal opened in 1848, flourished until 1900, closed in 1931, and deteriorated thereafter until resurrected as historically significant. It was dug by pick and shovel in 12 years for 6 million in dollars of the 1840s: its resurrection is an unending work in progress, costing more millions in dollars of the present. It now is both a state trail and a National Heritage Corridor, under dual jurisdictions of the Illinois Department of Natural Resources and the US. Department of the Interior (which doesn't really have to be understood to run on the path). Since its 55-mile length is impractical to cover either in a day's run or a single article, this is about the first 18 miles, from the trailhead to Morris.

This trailhead - where 1-55 crosses the canal, about 50 miles from downtown Chicago - is not officially even a trail access. It's a trailhead only for the moment and by default, pending restoration of the six miles north and east (where a more definitive one is foreseen). To find this transitory trailhead, drive south on the Interstate and spot the sign saying "Illinois and Michigan Canal." Keep going another mile south, to the freeway exit at US 6, which gives access to a frontage road back to the canal (which at this point seems just a ditch, nearly-dry and easy to miss). There's no sign to announce the trailhead. There's no parking lot, but it's rare that anyone parks here anyway. Just pull off the road and into the weeds, though not too far or there's risk of getting stuck. It's plain that hardly anybody begins the trail here.

The start of the path looks like the entry to a grotto: a small opening into transcendental wilderness. It promises transport into history from the weeds by the Interstate; though skeptics might wonder how history could sustain a viable running trail for 18 or 55 miles. But the path is for real - level, and well packed: a gravel surface so fine and firm as to be smooth even for cycling. For a runner it's a trail to cruise and experience - to run long at a steady pace with a strong sense of ambiance and hardly a thought for mileage. On this trail romantics run best.

The canal provides swampy water to run by, which makes this a great run if it isn't already (the theory being that all great runs must encounter either water or hills). The canal is still deteriorating naturally even as it is reclaimed synthetically - in effect subsisting on civil engineering as its life support - but it has been part of the landscape long enough to have established its preternatural presence in the order of things. It has the route of ametaphysical highway, though over 148 years it has moldered into the character of a metaphysical river, straighter and more subtly structured than streams that simply flow with gravity but still more organic than not. Part of the experience of running alongside is just getting accustomed to a waterway so well contrived and so accommodating to a running path.

All this becomes apparent in the first 100 yards or so. To run just this far is to experience the trail. To run farther is to savor the experience. And to run past the limit is to overdraw the enchantment - which means romantics have more stamina here than pragmatists and technicians.

And the trail does have pragmatic and technical faults. There are no mile markers; so there's no point in keeping time splits. Water bubblers are few; they tend to be off-trail in state parks and enigmatic places, and often they aren't working; so there's good reason to carry water. Toilets are equally rare and elusive, though their dearth is a lesser deprivation because deep woods proliferate. The only towns in the first 18 miles are Channahon and Morris, though Channahon is an abstract place where all the parts of a community can't seem to make a discernible, feasible town (not that a passer-by can readily find) and Morris is 14 miles farther down the path. Runners should presume that resources are not near at hand along the trail - and be thus forwarned or challenged or both.

But even after mundane inconvniences are acknowledged, the enchantment prevails, especially for runners who are hardened romantics. Four miles from the traifflead, the path comes to locks #6 and #7 and the dam across the Du Page River (near the abstract presence of Channahon). The locks no longer open, but they are preserved for historical significance. Above the dam, the DuPage widens into a reservoir from which some water fills the canal and some descends over the dam to the confluence with the Des Plaines; the trail crosses on a wood bridge. From here the strong sense of history predominates.

Downstream from the dam the path runs atop the levee that separates the canal from the Des Plaines River (which merges with the Kankakee within three miles, and the river thereafter is the Illinois), and one runs on the narrow earth wall between waterways of the past and present seeing barge tows on the river, herons rising from the reeds - perhaps the most captivating stretch of the trail.

(Still, it's rare to meet runners here: maybe only half a dozen thus far on a fine Sunday morning. For every runner there are perhaps 10 cyclists, and for every cyclist there may be 10 motorboats on the river: The good news is that the path is not crowded; the not-so-good news is that a whole lot of runners are missing out.)

Nine miles from the trailhead, canal and towpath veer away from the river, and for nine miles to Morris they are on a course roughly parallel to the river and about a mile north. The trail is now a long, straight rim: the path at any given point looks to be stretching miles ahead; it rounds a slight bend and stretches miles -the kind of miles on which there is so little sense of progress that even enchantment can begin to wear thin. Along the way is the Aux Sable Aqueduct, where the canal is conveyed over a bridge above Aux Sable Creek, and even the most dogged runners have to stop and admire the engineering curiosity of water channeled both over and under the bridge. (The only trailside drinking fountain is here, but it hasn't worked for some time.)

The path at last approaches Morris; it skirts outlying neighorhoods for yet another mile and finally rejoins the river near Stratton State Park, where motorboats are under a spectacularly high bridge. The park has prominent public toilets close to the path - equally spectacular after 18 miles on the trail, though not a fit finish to a great run.

A better ending: In Morris, an eerily silent, tidy town, there is food at Petey's Cantina, which appears to be the only place open on Sundays. It's three blocks off the trail, on Liberty Street, the town's main street. It's new, friendly, and clean; it offers free refills on large size drinks, and the enchantment is restored. Think of the mules toiling the same 18 miles hauling canal boats, which were 100 feet long and filled with grain, stone, sand, and coal.

Footnote to pragmatists and technicians. Free trail maps are available from the I&M Canal Information Center, P.O. Box 272, Morris, IL 60450; phone 815/942-0796. The maps show mileage and official access points, and they hint at locations of toilets and drinking fountains.

Footnote to everyone. At the National Heritage Corridor 25K race on September 15, the trail becomes one of the most rewarding of all race courses.