THE OBJECTIVE was easy. The execution was not. My quest to photograph the old 229-foot Chesapeake and Ohio Railroad Trestle Bridge leading to Sharp's Tunnel ended in a four-hour, 10.8-mile hike in West Virginia -- and no picture.

Sharp's Tunnel stretches for 511 feet around a bend beside the Greenbrier River, the longest free-flowing river in the eastern United States. At the tunnel's south end is the picturesque bridge I wanted to photograph as a memory of my hike.

The 77-mile Greenbrier River Trail parallels its namesake river. From Cass to Caldwell, this north-south railroad corridor once servedthe Mountain State's timber industry, when 3,000 miles of logging railroad crisscrossed the state. Soon after the corridor was abandoned in 1978, the C&O Railway donated it to the state of West Virginia. Once the ties and rails are removed, rail-trails are perfect venues for a variety of outdoor activities. They are wide and nearly level, two appealing characteristics for hikers and bikers. And since most run through remote areas, they're perfect for naturalists and those who love to photograph nature. (The best-known local example is Northern Virginia's 45-mile Washington and Old Dominion Railroad Regional Park.)

You can spend a day hiking the Greenbrier or a week exploring its many attractions. Three state parks, two state forests, numerous small towns and a myriad of historic sites are available to you. The Cass Scenic Railroad State Park, where visitors ride to Bald Knob in open passenger cars behind logging locomotives, anchors the trail's north end. About halfway down the trail at milepost 44 is Watoga State Park, West Virginia's largest park, and a favorite with campers.

Before starting my hike, I stopped at the restored 1901 Victorian Depot in Marlinton that now serves as a tourist information center to pick up a map and trail guide. Was there a way to reach Sharp's Tunnel other than hiking from the access point at Clover Lick, 15 miles north of Marlinton? I asked. From Clover Lick to Sharp's Tunnel is 5.4 miles. Carrying a heavy camera bag would only add to my misery. Was the time and effort worth it? I decided it was.

Early the next morning, I parked my car in a small clearing not far from the dozen or so houses that make up Clover Lick. Access points are indicated on the trail guide. Some, like the one in Clover Lick, are only small clearings, large enough for four or five cars. Those near Cass, Marlinton and Watoga State Park are larger, gravel-covered areas. (If you park your car at other than a designated access point and think it might be parked on private property, inquire at the nearest home and request permission to leave it there. It's the neighborly thing to do.)

In spring, you'll see redbud, dogwood and mountain laurel in bloom along the Greenbrier. Among the wildflowers beside the trail are Dutchman's breeches, trillium, squirrel corn, dame's rocket and lady's-slippers, to name a few. Wildflowers you may see in summer are rhododendron, black-eyed Susans, Queen Anne's lace, ox-eye, Joe-Pye-weed and wild bergamot. If you're hungry, there are blackberries for the taking. I hiked the trail in September, and a light jacket was barely sufficient on this brisk autumn morning. In a couple of weeks colorful fall foliage would attract more hikers, but at the moment I was alone.

Well, not completely alone. Black bear, white-tailed deer, wild turkey, Canada geese, osprey, wood duck and snakes are common here. The more elusive bobcat is seldom seen.

An hour later, a father and his young son cycled past me. More bikers than hikers use these longer rail-trails like the Greenbrier, the longest rail-trail in West Virginia and the second longest in the country. If you don't own a bike, rentals are available in several towns on or near the trail. Mountain bikes are preferable to touring bikes.

As the sun rose higher in the sky, so did the temperature. This trail that poses a minimal challenge to bikers is a bit more of an effort for hikers, especially in summer when it is often hot on the open gravel trail. Besides lunch, carry a water bottle; there's no potable water in the streams along the trail. Don't forget the insect repellent and sunscreen.

Finally the tunnel came into view. Instead of elation, I stared straight ahead in disbelief. The bridge was nowhere in sight. My longed-for photo op was on the other side of the tunnel.

I hadn't brought a flashlight and the thought of walking 511 feet through a narrow dark tunnel wasn't my idea of fun. Images of black bears, copperheads and rattlesnakes, all of which might inhabit this cave-like structure, quickly came to mind. On the other hand, after walking for two hours to get here, why not forge ahead. My courage failed me about 100 feet into the tunnel and I quickly retreated. Disappointed, I turned back toward Clover Lick.

About a mile from Sharp's Tunnel, a man proffered a greeting as he rode by on his fat-tired bicycle. Determined to make this trip worthwhile, I called out "Can I take your picture?" He stopped and introduced himself as Jack Snead, a retired Air Force officer living in Fort Washington. While Snead's wife was touring Greece, he was touring West Virginia -- by bike. My spirits rose a little when he agreed to let me photograph him cycling along the trail.

So I didn't get the photograph of Sharp's Tunnel. Once back home I even discovered there is, indeed, a public road popular with local fishermen that leads to the bridge -- the exact spot I wanted to photograph. But I wasn't disappointed. Who would be after a scenic hike in a peaceful, remote area of West Virginia?

These old railroads, once the lifeline of thousands of small towns, now provide recreational opportunities for millions of folks just like me. Only some of them carry flashlights. GREENBRIER RIVER TRAIL -- Marlinton, W. Va., is about six hours from Washington. Take I-66 west to I-81 south to I-64 west. From I-62 a few miles west of Lexington, turn north on Route 11 and then west on Route 39 to Marlinton. For a Greenbrier River Trail Map & Trail Guide that lists various access points, campsites, parking areas, and locations for groceries, post offices, public phones, meals and lodging, contact Watoga State Park, HC 82, Box 252, Marlinton, WV 24954, 304/799-4087 or call 800/CALL-WVA.) Carry water, snacks, a simple first aid kit and a flashlight for the tunnels.

Other sources for information include: the Pocahontas County Tourism Commission, P.O. Box 275, Marlinton, WV 24954, 800/336-7009 or check its Web site at http://wvweb.com/ www/pctc.html; or the Lewisburg Visitors Bureau, 105 Church St., Lewisburg, WV 24901 at 304/645-1000 or 800/833-2068 or check its Web site at http://wvweb.com/www/lewisburg. There is also a Web page on the trail itself at http:/wvweb.com/wvparks/ greenbrier -- rt/greenbrier -- rt.html.

Jerico's Bed & Breakfast (304/799-6241) near Marlinton is within a mile of the Greenbrier trail and also has four cabins for rent. Appalachian Sport (304/799-4050), also in Marlinton, rents bikes and provides shuttle service as does Jack Horner's Corner (304/653-4515) in Seebert (milepost 45.8). Elk River Touring Center (304/572-3771) in Slatyfork is a combination B&B, restaurant and biking center which rents bikes or can arrange guided tours. CAPTION: Other Rail-Trail Options

DON'T FEEL like heading out to West Virginia? Other rails-to-trails are closer, or offer different attractions. For information on rails-to-trails in general, contact the Rails-to-Trails Conservancy, 1100 17th St. NW, Washington, DC 20036; 202/331-9696. A national directory of trails, entitled "700 Great Rail-Trails," is available for $9.95, plus $4.50 shipping & handling. Their Web site is http://www.railtrails.org. CAPITAL CRESCENT TRAIL -- A recently opened 10-mile multi-use trail from Georgetown to Bethesda to Silver Spring. Public parking available only on K Street (near Key Bridge), at Fletcher's Boat House, 4940 Canal Rd. NW and in Bethesda (metered). Managing agencies are, for District: C&O Canal National Historical Park, P.O. Box 4, Sharpsburg, MD 21782, 301/739-4200; for Maryland: M-NCPPC, 9500 Brunett Ave., Silver Spring, MD 20910, 301/495-2535. A map of the trail comes with membership ($10) in the Coalition for the Capital Crescent Trail (CCCT), P.O. Box 30703, Bethesda, MD 20824, 202/234-4874. NEW RIVER TRAIL STATE PARK -- Virginia's longest rail-trail stretches 57 miles from Pulaski to Galax in southwest Virginia. (Two miles between milepost 17 to 19 closed.) Longest of three trestles is 1,100-feet, rising 50 feet above the river at Fries. Shot Tower Historical Park adjoins Foster Falls and serves as park headquarters. Picnicking, parking, river access and restrooms available at Foster Falls, centerpiece of the park and future campground site. Largest parking areas in Cliffview, Draper, Fries, Galax, Ivanhoe and Pulaski. Easily accessed from I-77 and I-81. Brochure available from New River Trail State Park, Route 2, Box 126F, Foster Falls, VA 24360, 540/699-6778. VIRGINIA CREEPER NATIONAL RECREATION TRAIL -- One hundred narrow bridges and trestles distinguish this 34-mile trail that runs from Abingdon to Whitetop Station, Va. Named for the steam locomotives struggling up its steep grades, the 15.9 miles of trail between Iron Bridge (milepost 18.4) to the Virginia-North Carolina line are part of the Mount Rogers National Recreation Area in the Jefferson National Forest. Map available from Mount Rogers National Recreation Area, Route 1, Box 303, Marion, VA 24354, 540/783-5196; or from the Abingdon Convention & Visitors Bureau, 335 Cummings St., Abingdon, VA 24210, 800/435-3440. WASHINGTON & OLD DOMINION RAILROAD REGIONAL PARK -- This heavily used 45-mile trail runs from Alexandria to Purcellville, Va. A 64-page, color W&OD Guide ($4.50 at the park authority; $5.75, including postage, by mail) that includes detailed map pages with symbols indicating bike repair shops, connecting trail systems, restrooms, restaurants and other trailside facilities is available from the Northern Virginia Regional Park Authority, 5400 Ox Rd., Fairfax Station, VA 22039, 703/352-5900. NORTHERN CENTRAL RAILROAD TRAIL -- A scenic 19-mile trail from Ashland, Md. to the Maryland-Pennsylvania line. Southern end of trail parallels the Big Gunpowder River. Abraham Lincoln traveled on the Northern Central en route to delivering his famous Gettysburg address; after his assassination, these same rails transported his body to Harrisburg, Pa. For a map, send a self-addressed, stamped envelope with your request to Gunpowder Falls State Park, P.O. Box 480, Kingsville, MD 21087, 410/592-2897. BALTIMORE AND ANNAPOLIS TRAIL -- This 13.3-mile trail follows the route of the Old Baltimore and Annapolis Railroad from Glen Burnie to Maryland's capital. The first Maryland trail to be chosen as part of the East Coast Greenway, the nation's first long- distance, multi-user trail eventually stretching from Maine to Florida. Map available by sending a self-addressed stamped envelope with your request from the B&A Trail Park, P.O. Box 1007, Severna Park, MD 21146, 410/222-6244. Next week in this space: In Motion goes sea kayaking. CAPTION: Jack Snead, of Fort Washington, Md., pedals along the Greenbrier River Trail near Sharp's Tunnel in West Virginia.