WHERE: The Sunday Source's Metro train trip returns, this time exploring 13 of the 26 stops along the Orange Line (don't worry -- the other half will get its due in time).

WHY: A NASA library in Southwest, a secret notebook among graves and crab cakes with lots o' lumps.

HOW FAR: 10.14 miles, or 26 minutes without stopping.

With a full day's journey ahead -- remember, Metro runs till midnight or later -- start your Orange Line adventure with a full belly and a cushioned spine at the Ronald Reagan Building and International Trade Center at Federal Triangle. Down a staircase that would make Scarlett O'Hara swoon is a food emporium with menus all over the map. Give in to your hankering du jour -- Mexican, Mediterranean, New York deli -- then dash up to Wilson Plaza and score one of the best seats in the house, a white plastic lounger that resembles a space-age dentist's chair. Since the coliseum-shaped plaza is open from sun up to high moon, you can watch the sky pass through its many moods from your 45-degree perch.

But don't laze about too long; instead, go read the trees at the U.S. Department of Agriculture. Even with the madness of the Mall and Smithsonian swirling behind you, you can still feel the gravitas of the plaque-adorned arbor that honors Martin Luther King Jr., holocaust victims and 13 USDA employees who died in grain elevator explosions in 1977.

Bland architecture masks the out-of-this-world wonders inside the little-known NASA Headquarters Library at Federal Center SW. Upon entering -- wear that visitor's pass with pride, because you have to give it back -- staff members will greet you, eager to answer any Trekkie question. Or, seek out the discovery yourself: The maze of books and magazines may not make a lot of sense to those without an astrophysics degree, but the shuttle and space station models bring out the gee-whiz in all of us. When your brain is baked on rocket science, pop in a video -- how about "Apollo 13"?

Uncover mysteries of a different sort at the Supreme Court, near Capital South. Mainly, will John Roberts replace Sandra Day O'Connor? And do the justices eat in the downstairs cafeteria, which serves up a mean bowl of Froot Loops? (Answers: who knows, and not likely; the justices dine elsewhere.) Until the party of nine returns in October, the court is open to all for tours. Leave time for the short docu-flick, the portrait gallery of past justices and the gift shop, where you can buy Hummel-like figurines of law clerks.

The Stadium-Armory stop is still in the city, but the historic Congressional Cemetery feels more like pastoral West Virginia. You can actually hear the leaves rustle -- or are those the Ghosts of Congressmen Past? Just beyond the Native American totem poles, a little yellow notebook is neatly tucked beneath one of the twin benches lining the walkway. Visitors have scrawled poignant reflections into the journal, such as the tear-jerking passage written by a gay man who once considered suicide. Such unbridled emotion might inspire you to pen your own ponderings -- a writing utensil is provided, so you have no excuse.

Across the Anacostia River, Miss Charlotte's takeout joint on Minnesota Avenue serves "monster" burgers, but her specialty comes from the ocean. If you are new to crab cakes, here's the dish, courtesy of Miss C.: Lump cakes are like filet mignon, jumbo and regular are like sirloin. Next stop: the Kenilworth-Parkside Community Center at Deanwood, which has just about every ESPN activity short of steeple chasing -- and it won't set you back a dime.

At Landover, the penultimate station, art and inspiration are underfoot. The sidewalk along Pennsy Drive is decorated with colorful tile designs and insightful quotations. And for your return from New Carrollton, this Arthur Ashe quote seems especially apt: "I have always drawn strength from being close to home."

-- Andrea Sachs

Metrorail's One Day Pass costs $6.50 and is valid weekdays after 9:30 a.m. and all day on weekends and federal holidays, until the last trains depart. Passes are available online (www.wmata.com) or at the electronic kiosks in all Metro stations.