Greenbelt. It is very easy to get to and very well patroled. It is the closest station you would reach coming from BWI. Just hop on 95 S to 495 (south or east...I forget what the sign says now). It's the second exit I believe and very well marked.
I have used it many times on weekends. Even if you are used to driving in DC, it is the most hassle-free way to go for sightseeing. There is stop right iiin the middle of the mall so you come out in front of the museums. Just need to be aware of hours. I forget how late the trains run on weekends. They can also buy a metro day pass (I believe) that would allow them unlimited use for the day.
[This message has been edited by tazi (edited 09-30-2002).]
[This message has been edited by tazi (edited 09-30-2002).]