IT'S TIME ONCE AGAIN for the big show. The trees in ShenI andoah National Park, that miracle of unspoiled land the state of Virginia presented to the federal government back in 1936, are wrapping themselves in the fiery colors of autumn. Old Rag Mountain is shrouded in the blue mists of the season and the migratory birds have departed. The insect world in the forest is quiescent and the autumn sneezeweed and witch hazel are vying with the late asters for notice. The Shenandoah is in its finest hour.

Rte. 66 is the magic carpet that takes you to the park gates behind which deer, bear, fox and bobcat dwell in this sanctuary. The Skyline Drive, the 105-mile highway in the clouds that takes you down the spine of the mountain ridge, is getting crowded. And no wonder. What a panorama is laid out from the car window -- the Blue Ridge, the Piedmont, and to the west, the Shenandoah River valley and the Alleghenies!

The drive itself is well worth the trip from Washington, but stay the weekend and you'll have time for nearby attractions that you might otherwise never see. Like, for instance, Skyline Caverns, which will never put Luray in the shade but which, if you are as lucky to have a guide like I did, offers a diverting break when you tire of mountain grandeur.

Skyline Caverns is a Johnny-come-lately compared to Luray. It was discovered by Dr. Walter S. Amos in 1937, when he was on a surveying trip of the area. Its main claim to fame are the anthodites, mineral flower-like clusters that cling to the roof in a special chamber and are seen nowhere else in the world. But the real fun is the tour you get, the guide's patter, the kitsch performance with colored lights and organ music, and the enthusiasm with which you are guided through Dr. Amos' wonderland.

Troy was the guide who fell to our lot, and the best thing that could happen is that you should be so lucky. In an accent rich with the twang of the Virginia hill country, Troy instructed us in the splendors of his underground domain, shepherding us through like a combination benevolent pedagogue and circus barker. Could we not see that the Capitol Dome formation also brought to mind an elephant's foot stuck in chewing gum? Didn't we see in Rainbow Lake the setting of an old Walt Disney movie? And, by the way, did any among us know what a grotto is?

The anthodites hang from the ceiling in a special temperature-controlled room two degrees warmer than the rest of the cave. They look a little like delicate white sea urchins and are said to be 160,000 years old. They grow an inch every 7,000 years and Troy, hand on the light control switch, bathed them successively in red, white and blue lights. Virginia state law protects the caverns and its mineral formations from paint, which may be fortunate.

You walk 1 1/8 miles and it's cool down there below the earth's surface, 54 degrees year-round, so wear warm clothes. You cannot just look a little and return quickly to your car, because the lights are snapped out as you pass through the caverns and you are captive for just under an hour. But then, you wouldn't want to miss the performance of God in the Mountains in the Cathedral Room anyway, and that is a late climax of the tour.

The Cathedral Room is an impressive natural grotto laced with narrow crevices affording a glimpse of tons of rock overhead with a collection of stalactites hanging above a miniature mesa adorned with odd formations. God in the Mountains is a disembodied voice rising above organ music to caution us all to remember that nature's wonders must not be lightly taken in the advance of civilization. Pink glows appear and disappear.

Tour groups are taken through every 15 minutes from 9 a.m. to 6 p.m. until the end of October, and 9 to 5 p.m. for the remainder of the year. Tickets are $4. (Ask for Troy.)

When you emerge, you may well be ready for some creature comforts, and the Hotel Strasburg in Strasburg is handy. Staying overnight in this town of about 500 people could make you put away your stress pills. The Strasburg is a charmer and, if you are not too much of a stickler for gourmet food, there's no nicer way to spend a nearby weekend.

An old Victorian hostelry furnished with the beaded lamps, steel engravings and romantic plaster figures of the period, the Strasburg is as easygoing as the old-timers sunning themselves in front of any of Virginia's small-town courthouses. Your room key at the Strasburg fits the front door as well, and you'll need it because after 10 p.m. the hotel locks up.

The food is country simple and lacks verve, but the service is pleasant and the setting delightful. Stern, eagle-eyed men and women of an earlier generation stare down from oil portraits on the wall above the potbellied stoves which adorn many of the downstairs rooms. Upstairs, the rooms are furnished with antiques, and the bathtubs -- down the hall -- are claw-footed. The little bar to the right as you enter is devoted to railroad memorabilia and guests sometimes sit down and play the old upright piano. Nice place, the Hotel Strasburg. Seventeen rooms, most with shared bath, $30 to $35 per room. For hotel or restaurant reservations, phone 703-465-4140.

This area is an antique buff's paradise and Strasburg is proud of its Emporium, a collection of antique stores, flea markets and craft shops all under one roof. You'll see everything here, from nice hand-turned pottery (for which Strasburg was originally famous) to real junk in some of the flea markets. Auctions are held here the first and third Sundays of each month at 1 p.m. Hunting for American "country" and advertising items can be especially fun.

Drive down the Skyline when you finish at Strasburg to Dickey Ridge Visitor Center, not quite five miles south of Front Royal. There's a nice trail leading out from the Visitor Center, where touch-and-feel exhibits like snakeskins and a barred owl wing are on display along with handsome wildlife photos. You can get a map of the nearby territory at the desk.

Elkwallow, almost 20 miles down the spine of the Skyline, has gifts like pottery, baskets and jams for sale. Six miles later you can get off at Thornton Gap and swing home by Rte. 211, a pretty twisting road bordered by neatly mowed hayfields, roadside apple and cider stands and a breathtaking panoramic view of the Blue Ridge.

Antique hunters should stop in Sperryville to case the six antique shops clustered there. Fairlawn Antiques in the big, white main house down the road is a find, though prices are not cheap. Everything in 12 rooms of the house is for sale, and every available space is crowded with knickknacks, old glass and relics of the 18th and 19th centuries. Stoneware jugs line the stairs to the second floor and patchwork quilts (oh, those prices!) drape the stair railing. The house black cat sleeps away the hours in one of the handsome old beds, and it's all great fun. Lesser treasures like ancient cash registers and a WAC uniform from World War II are found in the slave quarters and barns behind. Nobody bothers you while you browse.

Summer fruits have vanished from the roadside stands on 211, but several different types of apples grow in the area and are displayed for sale everywhere in huge baskets. The smell is wonderful and the price is right.