Have NO windows
Why?
Just what kind bizarre rituals are they trying to hide?
There are two main kinds of Mormon buildings—meetinghouses, and Temples.
The vast majority of activity takes place in the meetinghouses. These are our regular “churches”. I've never seen or heard of a meetinghouse that didn't have windows (although they are nearly (but not always) of a frosted or textured glass through which one cannot easily see much), and in any event, the meetings that we hold there are open to the public. If you think we're hiding anything, feel free to come visit a meetinghouse any time we're meeting there and see for yourself. If you're expecting anything bizarre or sinister, then I'm afraid you're going to be very disappointed.
I cannot extend that same invitation regarding the Temples. Only members of the church in good standing are allowed therein; and we do not discuss, with outsiders, the details of the ceremonies that take place there. Many have taken this as license to make up all sorts of crazy accounts of bizarre and sinister rituals that they claim to take place therein. You can search the Internet for accounts of these rituals, but you'll find far more falsehood than truth. All I'll say beyond that is that the more bizarre an account seems, the less likely it is to be true.
As for the Jehovah's Witnesses, I can't really speak for them. Perhaps they prefer MacOS, or some version of Linux.