As you might guess from their name, they take the concept of "community" seriously
Third Place has two locations, I am only familiar with their store in Lake Forest Park. And what a treasure it is!
Third Place is one of the few book stores which shelves both new and used books together. Possibly the only such store in the Seattle area that I am aware of. (I don't count Half Price, which only stocks discounted new books.) Powell's in Portland is the only other store I know of with this practice, and of course we all love Powell's.
What is great about this practice is that you can choose which version of a book you want - full price, or used? You can compare the two editions, examine the condition, and decide if it's worth it to buy the new one, or save a few bucks and get the used one. And it also broadens the scope of the books that they stock, because it opens the floor up to a much wider source of books: the reading public.
Naturally, Third Place also buys used books. The used book market has really collapsed in the last few years. You used to be able to count on recouping some of your losses by re-selling the book used, but that is no longer the case. However, Third Place is one of the few places that still offers you a bonus if you choose store credit - 50% more than the cash value. It's definitely worth it!
My first experience with Third Place was attending an author reading many years ago. I was surprised when I turned up, expecting the usual crowding of chairs in an aisle, and found a proper stage with chairs spread out on the floor auditorium-style. Third Place has the space and the experience to do a reading right! If you ever have the chance to see an author reading there, I recommend it.
Third Place is attached to a large open food court-ish area called the Commons. They offer free wifi, and tables that you can sit at for as long as you like without getting the stink-eye from employees. When I lived in Lake Forest Park, I spent countless hours at the Commons, reading and sketching and goofing off on my laptop (just like everyone else).
And finally, Third Place is one of the few independent bookstores that sells eBooks. They currently offer 12 popular eBooks at only $5.99 apiece! (They use Google eBooks, the EPUB format. If you have a Kindle, you can convert these to Kindle format using the Calibre.)