Take advantage of the unseasonably nice weather by enjoying one of the more compelling outdoor spots around the city. Among them:
* Pohick Bay in Mason Neck, Va. and Bull Run in Centerville, Va. -- Largest swimming pools on the East Coast. Admission: $1.75 for children under 12 and grown-ups over 59; $2 for others; children under 2 free. 278-8880 weekdays, 339-6100 weekends for Pohick, 631-0552 for Bull Run.
* Theodore Roosevelt Island (entrance on the Virginia side of the Potomac) -- Deeply wooded and serene. 426-6922
* C & O Canal, Georgetown to Great Falls -- Ride the barge from the dock at 30th and M Streets, bike or stroll on the tow path, visit Great Falls in Virginia or Maryland where the Potomac River drops more than 70 feet over falls and rapids. Barge information, 299-3613; ride schedule, 299-2026; Great Falls Park, 759-2925.
* Lake Needwood in Rockville -- Rent a rowboat or paddleboat or go fishing. 762-1888.
* Catoctin Mountain Park, Thurmont, Md. -- For a touch of presidential cool: Camp David, although not open to visitors, is nestled in this wooded park. Free public programs: whiskey-making demonstrations, Friday and Saturday night campfire programs, Saturday afternoon "family walk," Sunday morning "children's walk." (301) 663-9330.
* Cunningham Falls State Park, Thurmont, Md. Rock-climb to the 40-foot falls. (301) 271-7574).
* Drainesville District Park, Va. -- Where Scott Run ends in a refreshing waterfall. 941-5000.
* Fountainhead, Fairfax, Va. -- Boat and fish on the widest point of the Occoquan River. 250-9124.
* Lake Accotink, Burke Lake and Lake Fairfax, Fairfax County, Va. -- Rent boats, fish, ride the carrousel. Accotink 569-3464, Burke 323-6600, Fairfax 471-5414.
* Luray (Va.) Caverns -- Bring along a light sweater or jacket. (703) 743-6551.
* Rock Creek Park in Northwest -- Four-mile-long, one-mile-wide patch of city cool. 426-6834.