2 - I'll be arriving into WAS on the Silver Meteor (est 7:46AM) and departing on Capitol Limited (est 4:05PM). I've never been to DC and I'm looking for suggestions of things to do and sights to see. I am not opposed to walking, bussing, or taking a cab or Metro subway.
I just got home from a few days of playing tourist in DC. One of my favorite buildings was the Library of Congress. It's about a 10-15 minute walk from Union Station straight down 1st Street NE (which becomes 1st Street SE as you approach the beautiful main entrance to the building - you'll pass the Supreme Court building on the way). It's much more than a library. The main building that most people are familir with is the Jefferson Building. It's a beautiful work of architecture, art and design. The inside reminded me of a fabulous museum. So much detail in the floor, the walls and the ceilings. If you go, do everything you can to sign up for one of the free 1-hour guided tours. The tours start at 10:30, 11:30, 1:30, 2:30 and 3:30. Sign up 30 minutes early on the lower level. Our docent was extremely knowledgeable and imparted so much detailed knowledge of the history of the building that we never would've picked up on our own. I was hoping to walk through the huge main reading room, but that's only open to people doing serious research. But, on the guided tour, we got a bird's eye view of the room from the building's second floor. After the tour, we walked across the street to the other building that makes up the Library of Congress - the Madison Building. There, we applied for and received an official LOC reader's card, which is free and is required for admission to any of the smaller reading/research rooms in either the Jefferson or Madison Buildings. Makes for a nice souvenir.
Back in Union Station, I second the idea of storing most of your luggage in the Club Acela lounge for the day while you go exploring around town. There is a storage area just behind the reception desk just as you enter the lounge.
Also in Union Station, if you're just looking for something quick to eat, there's a humongous food court on the lower level. All the typical fast food joints plus a whole lot more.
If you're looking to venture farther away from Union Station and you're not up to walking, consider taking the Metro, DC's subway system. Most fares within the city are about $2 or so. There are Metro stations within fairly close walking distance to most of the popular museums and monuments. Except the Lincoln Memorial. For some reason, it's at least a mile walk from the nearest Metro station to the Lincoln Memorial (unless I seriously misread my maps).
I also went to the John F. Kennedy Center for the Performing Arts. A beautiful, modern building housing several performance halls. Similar in a way to Lincoln Center in New York. Free guided tours are also offered here, starting every 10 minutes or so. This is a LONG walk from Union Station, so if you want to go here, I would suggest taking the Metro to Foggy Bottom, where you can pick up a free shuttle bus to The Kennedy Center. The shuttle buses are red, and run every 15 minutes. When you're finished at The Kennedy Center, the shuttle bus will take you back to the Foggy Bottom Metro station.
The intrusiveness of the security checks depends on the building you are entering. At the Library of Congress, we had to empty our pockets of all electronics, change, keys and other metal objects. We also had to open the zippers to our bags, although security only took a cursory glance into them. At the Air & Space Museum, we only had to place our bags in a bin, which then went through a scanner. No emptying our pockets or opening pockets in the bags. At the Museum of the American Indian, I had to open the pockets in my bag, then the security witch took a long, thin plastic rod and poked and prodded all through my bag to make sure I wasn't entering with any contraband. It's because of this nonsense that I no longer fly! At the Lincoln Memorial, there is no security check. You are free to walk up the steps, into the statuary hall and gaze at Honest Abe as long as you want.
Anyway, that's a little taste of what we did over 3 days. You can't do it all in one day. Don't even try. Focus on one or two things you are most interested in and save the rest for future trips. Enjoy your trip.