'Tis the day after Christmas and all through the house . . . kids. School is out. It's a holiday, after all. You deserve to get out of the house and do something you don't have to work at or pay for.

To lift you from under the wrapping paper avalanche, the Smithsonian's Museum of History and Technology has planned a week of special activities. From Dec. 26 through jan. 1, visitors will be serenaded - with antique instruments, by barbershop quartets, with opera and gospel music. In various nooks of the museum, you can watch others do the work, for a change - a nutcracker-carver who first learned to whittle when he was 6, experts in casting and painting toy soldiers, dollmakers and pinata-makers, puppeteers and jugglers.

Starring on the second floor, the showpiece of the celebration, 12 trees of Christmas, branches laden with all sorts of make-your-own decoration ideas.

It'a a chance to go to the movies for free. Three seasonal films will be showing in the auditorium throughout the week: "The Wizard of Oz" starring Judy Garland, Walt Disney's "Hans Brinker," and "A Child's Christmas in Wales" narrated by Dylan Thomas.

For a recorded daily schedule of holiday events at the Smithsonian, call 737-8811.

Now that you've taken care of the kids, think about yourself. Time to relax, meditate and prepare for the new year. Go somewhere quiet to commune with yourself. Somewhere warm.

Just about this time, you may yearn for a reminder of spring - anything green except Christmas trees. The Bureau of Engraving may be a too-harsh reminder of recent extravagances, but the refreshing green of the Botanic Gardens at the southwest corner of the Capitol grounds is a lush jungle.

This time of year, hundreds of poinsettias - red, pink and white, with names like Bavarian pinwheel and Jinglebells - make their home in the front hall and east and west wings. It's a nice place to sit down, check out bromeliads, orchids, cacti and ferns, listen to the indoor streams and waterfall, and think.

The garden is open 9 to 5 everyday except Christmas and New Year's Day. Admission is free.

Other poinsettia profusion can be seen at the Washington Cathedral, where they grow their own. A sublimely restful place, the cathedral has tours every day from 10 to 3:15, starting near the Wisconsin Avenue entrance. Sundays, tours start after the 11 a.m. service. You think you have problems - you'll forget them as a docent enumerates troubles encountered in building the world's last cathedral. And it's not finished. Stone carvers are still at work, as you can see if you visit Monday through Thursday.

Some people can only withdraw from the holidays gradually. They've become shopping-addicts, can't touch anything without turning it over to look for a price tag. These generous and exhausted souls are commended to Georgetown now, to stroll and people watch. To windowshop while stores are at their festive best and the Christmas press is over. To stop in at Yes! on 31st Street for this health food cafe's one concession to diet - delicious coffee, sweetened with honey instead of sugar.

Up on M Street, inveterate shoppers can drop in on "everything must go" sales. Two buildings, 3222 and 3248 M St. NW, are having their insides cleaned out to make way for the triple-storied Georgetown Square mall. part of the old Capital Transit carbarn, the historic facade of these buildings will be preserved. Behind it, shops for gems, trinkets, rugs and clothing are closing out to meet a January deadline.

The historic streets of Old Town, Alexandria, also should be worth visiting, once shopping crowds clear. George Washington Bicentennial Center, at 201 S. Washington St., puts the town in perspective. It's a museum that explores the role of Virginia and Virginians in Revolutionary times. On Wednesday, Thursday and Friday after Christmas, two free films are showing, "The Music of Williamsburg" and "The Colonial-Naturalist." For showtimes, call 750-6677.

As long as you're learning about Founding Fathers, George Mason's Gunston Hall Plantation is just down the road, south of Alexandria on Rte. 242. Overlooking the Potomas, the house's construction was begun in 1755 by George Mason. Called by Thomas Jefferson "the wisest man of his generation," Mason authored the Virginia Declaration of Rights.

His house is especially lovely now, decorated for the holidays in late-18th century fashion. Open 9:30 to 5 every day but Christmas. Admission $2 for adults, 50 cents for children 6 to 16, and under 6, free.