If you're looking for a romantic and inexpensive weekend away from the city, the rolling farmland of the Cumberland Valley in south central Pennsylvania is the place to go -- especially this weekend or next, when the Adams County Apple Festival is on. And the place to stay is the old Byron mansion, the Mercersburg Inn.

The best part of our recent visit was a tour with the owner and manager, Don Clevenger, a tall, friendly man in his early 40s. We climbed up and down staircases and into odd corners and heard history, rumors and gossip about the house, the town of Mercersburg and the Byron family.

Rumor has it that Mrs. Byron wanted the fanciest house in town, and Mr. Byron ran a prosperous tannery. The result of the union was a 17-room mansion: among its appurtenances, a 92-foot-long, two-lane bowling alley, a two-door elevator, a servants' wing and a caretaker's cottage. In 1910, it was $50,000.

After the Byrons died, several decades later, the house was put up for sale, and since 1952, it's been a hotel.

We started on the first floor, passing through ionic columns to enter a tiled vestibule, and from there into the grand central hall, where there are more columns -- of Italian marble. Dual curved staircases lead to the second floor. The balustrades are of heavy handwrought iron, made by a local blacksmith named Taylor. He was a good friend of Mr. Byron's and -- according to Byorn descendants -- his drinking buddy. A trapdoor on the third floor leads to the attic where reportedly they kept their bottles and escaped for a nip.

The high-ceilinged public rooms on the first floor range from the simple and elegant living room with oak parquet floor and brick fireplace, built, they say, by a German mason imported for the task, to the richly carpeted formal dining room.

Clevenger is convinced that old Mr. Byron hid something somewhere in the walls of the house, and this room seems a likely location. There's a suspicious place where otherwise perfectly matched mahogany paneling doesn't match. On the other side of the wall in the next room is a closed-off fireplace. In a house with seven fireplaces, mused Clevenger, why build six that work and one that doesn't? So one of his projects is to discover the cache of "whatever it is" that he is sure is there, somewhere.

On our way to the basement steps we passed the conservatory with its translucent glass roof. Mrs. Byron would probably be distressed to learn that this has become the hotel office. From the basement to the second floor are two sets of stairs -- one for the family and one for the servants.

The basement has been altered with the changing times, so the 92-foot-long bowling alley is now a 92-foot-long party room. The pieces are still there, stacked up for nonbelievers. The home vault is still there, too, both steel doors intact, the concrete interior designed for maximum security: Nowadays, the steel and concrete protect the inn's liquor and wine supply.

Around the corner, Clevenger showed us the elevator -- not your ordinary, run-of-the-mansion type, but a two-door model.

We climbed the back stairs to the second floor, where the servants comfortable quarters used to be: Their rooms now count among the 14 large bedrooms of the inn. In the master bedroom suite, the bathroom still has its original fixtures, in marble, procelain and brass. One of its bedrooms has a balcony and the other has a porch.

When you're not just relaxing, there's lots to see en route and nearby. Frederick is a nice stop on the road from Washington, as are the Catoctin Mountains, where Camp David is. Gettysburg Battlefield, too, is good for several hours' visit. There are fruit stands and orchards, antique shops and ancient, crumbling cemeteries and in between, gentle rolling farmland.

The first two weekends in October, nearby Adams County puts on an Apple Harvest Festival, an old time country fair with food, entertainment, local crafts and apple butter making.

For winter vacationers, there's skiing a short distance away, near Fannettsburg on Route 75.

The Mercersburg Inn fits perfectly into this subdued countryside which in many ways has been bypassed by the 20th century. It's no Howard Johnson's -- no TV sets, no ice machines at hall's end and no room service. Just turn-of-the-century elegance. And peace and quiet. TO GET TO THE INN Take I-270 to Frederick, then I-70 to Hagerstown. Go north on I-81, past the Pennsylvania line, then west on Route 16. The inn is just before you enter Mercersburg, at the intersection of Routes 16 and 75. Rates are $15 for a single and $20 for a double.

If you don't want to spend the night, lunch, dinner and Sunday brunch are served in either the formal, mahogany-paneled dining room or on the informal, enclosed proch.

Phone: 717/328-3412. AND ON TO THE FAIR The Adams County Apple Festival happens this Saturday and Sunday, and also October 13 and 14, from 11 to 6. It's on the South Mountain Fairgrounds about 10 miles north of Gettysburg on Route 234, west of Arendtsville. Admission: $2 for adults; 12 and under, free. Phone: 717/677-9413.