It is a very long walk from one end of the National Mall to the next, but if you can do it there are a ton of sights along the way. The WWII and Vietnam memorials, as well as some others. It is also a great walk to get pictures and great view. There are some resting spots and bathrooms along the way, closer to the Lincoln and Vietnam Memorials. There really is not a great spot for the Vietnam memorial end of the mall to get off the metro but I suggest using the Smithsonian stop and taking the walk, more so if the weather is nice.