Since Washington lies at the fall line--where the Piedmont Plateau drops to sea level and gives way to the coastal plain, in geography-book jargon -- we've got a few waterfalls. Some are just for looking at, while others you can really dip into -- literally.

The big daddy of area falls, of course, is the GREAT FALLS of the Potomac. In its own way, this local celebrity surpasses the great Niagara itself: When it's at its fullest, 480,000 cubic feet of water tumble over Great Falls every second, and that beats Niagara's flow. It's just about as dangerous as Niagara, too, so don't go near the water. The Edgar Kaufmanns of Pittsburgh so loved the rush of the waterfall on Bear Run in Pennsylvania that they had Frank Lloyd Wright build them a house astride the falls. It's called FALLINGWATER and is built in, around and over the falls. There's even a stairway from the living room straight into the water below. For reservations to tour the house -- a four-hour drive from Washington -- call 412/329-8501. Just about every river and run falls somewhere around here. There are nice falls on FOUR MILE RUN upstream from Columbia Pike and Arlington Mill Road in Arlington, for example; ROCK CREEK falls, albeit rather gently, between Military Road and Peirce Mill. The mighty RAPPAHANNOCK cascades near Fredericksburg, upstream from I-95, while the OCCOQUAN RIVER has its falls between Lake Jackson and Occoquan west of I-95. A lovely falls is that of the James River at Bell Island, part of JAMES RIVER PARK in Richmond. There's also water running down the Blue Ridge in gorgeous gorges just a short hike on well-marked trails from the parking lots of SKYLINE DRIVE. In Maryland's Switzerland -- the Deep Creek Lake area of Garrett County -- there are two famous falls, SWALLOW FALLS and MUDDY CREEK FALLS, both in Swallow Falls State Park. If you don't mind a people-produced waterfall, amble over to the National Zoo and feast your eyes on the 21- foot cascade that tumbles from the rocks on MONKEY ISLAND. You can't get to it, but it should cool you off just to watch the island's resident macaques basking in its spray. The people who built Columbia, Maryland, dammed up the LITTLE PATUXENT RIVER to make a lake but they made the dam look like a real waterfall, rocky ledges and all. This is a recycling waterfall, however, with a fire-hose-like device that sends the water back up to the top. A more studied and symmetrical fake waterfall may be enjoyed in MERIDIAN HILL PARK on 16th Street, where 13 falls of graduated size flow down terraces into a graceful basin. Perhaps the most sybaritic waterfall around is the one that flows inside the NATIONAL GALLERY, under glass, just outside the Cascade Cafe. Here's a waterfall you can enjoy in air-conditioned comfort while sipping a cold drink.