Pearl Street is the main drag. It's essentially a college town although a fair bit of tech has moved in. It's actually pretty walkable but Boulder is very protective of open spaces and conservative about growth generally so you're not going to see anything like a dense urban core. Somewhere like Ithaca NY isn't that different.

Of course, you wouldn't want to live in Boulder without a car. Pretty much the whole point of being there is to get into the mountains.