Actually, some Kingdom Halls do have windows. Others do not have windows because of cost and for the sake of security. Generally, a Kingdom Hall is built without windows in areas which tend toward hate crimes and vandalism against houses of worship.
Pictures of some Kingdom Halls that *do* have windows:
http://defendingjehovahswitnesses.blogspot.com/2011/09/windows-and-kingdom-halls-of-jehovahs.html
We invite all interested ones to attend meetings with us at our Kingdom Halls. Just contact your local Kingdom Hall for times.
From the Jehovah's Witnesses Official Web Site:
"Jehovah’s Witnesses hold meetings for worship twice each week. (Hebrews 10:24, 25) At these meetings, which are open to the public, we examine what the Bible says and how we can apply its teachings in our life.
Most of our services include audience participation, much like a classroom discussion. Meetings begin and end with song and prayer.
You don’t have to be one of Jehovah’s Witnesses to attend our meetings. We invite everyone to come along. Seats are free. No collections are ever taken."
Full Article:
http://www.jw.org/en/jehovahs-witnesses/meetings/
Also see:
Why do Jehovah’s Witnesses meet together? What happens at those meetings? And what do visitors who are not Jehovah’s Witnesses say about the meetings?
http://www.jw.org/en/publications/magazines/wp20090201/invited-to-the-kingdom-hall/