Conversation so far:
What is worth seeing in Washington D.C.?
Most prominent at its center point is the Washington Monument, and war memorials include those to veterans of World War II, the Korean War, and Vietnam. ... If you look at a Washington, D.C. attractions map, you'll notice that many of them line the National Mall, so you're likely to spend a lot of time here.

Question: Which Smithsonian museums are the most popular
Self-contained rewrite: Which Smithsonian museums in Washington D.C. are the most popular?