Harrods is a must-visit department store, and one of those places that takes longer than you expect to really explore. The book section is incredible, and it sounds weird, but be sure to take the Egyptian Escalator. Here's my biggest pro tip, though: don't have tea in The Tea Room, it's dark and crowded; instead, enjoy it out on the terrace of The Conservatory on the top floor. (Or better yet, have a glass of Champagne.) There aren't as many options, but you can still do an afternoon tea with scones, and the views are much better.