It's worth winding around the lovely but poorly marked lanes of Columbia, Maryland. It's even worth slogging your way through the evening rush hour.

Once you've arrived at Merriweather Post Pavilion, once you're in the cozy, open-ended auditorium or the adjoining, arbored apron, it becomes apparent that it's a terrific place to enjoy a summer concert. Courteous ushers wearing shorts and bearing flashlights show you to your seat; kids sit having picnics or enjoying snacks bought from the wooden hut down the tree-shaded lane; sweethearts loll on blankets, their murmurs blending with cicadas in the trees. It's all vaguely reminiscent of summer camp, except, of course, the entertainment's usually much better.

Parking's included in the price of the ticket, which varies according to who's on stage and whether you're sitting on the lawn or in the pavilion. Almost all concerts begin at 7:30, which means those traffic hassles. But once the sun begins to go down and the music comes up, it's one of the great outdoor entertainment experiences in the Washington area. POST PLEASURES -- While Merriweather Post has a reputation for hosting a lot of rock acts, this summer there'll also be performances by jazz artists, country singers and even comedians. For information on tickets and schedules, call 982-1800.