Trafalgar Square is the perfect example of this, only it's a giant square that is a hot tourist attraction. People just come to hang out, eat lunch, wander around, take selfies, and meet friends. It's loud + energetic, and there is always something to look at. Despite the traffic + crowds, I love the local artists that entertain tourists. They're a little quirky and seem to have too much time, but every once in a while, you get thoughtful + colorful pieces of work like the one above.
The other great part to Trafalgar Square is that its home to the National Gallery, a free museum with jaw-dropping art {which is on my to-visit list}.