Obvious D.C. highlight #42: Lincoln Monument.Old, historic, crowded. Still beautiful.Even, perhaps, a learning experience.On the National Mall, monument central, it takes only a little imagination to dodge the crowds for a few moments and enjoy it all in peace and even quiet.Go back at night, though, for an entirely different experience.Not totally empty, perhaps, but such a different look and vibe that it seems almost like a different building from the one you saw earlier in the day.Throw on some warm clothes, take a spare battery pack, and shoot your heart out. Night on the National Mall is definitely the time for photographic exploring.