I haven't seen a religious building this imposing since leaving Russia. It's definitely worth a visit if you're in the area, whether or not you're a Baha'i seeker. It's open to the public. Fair warning: if you go into the lower level, dudes will try to proselytize you. They're really nice and all, but if you're not keen on that, I'd recommend sticking to the temple itself and staying out of the basement rooms.
visit the Bahai temple in Wilmette (northern suburb)
The architecture (and grounds) are wonderful, plus you can get a good look at a quiet little suburb of the big city of Chicago. It's a completely different atmosphere.
Maybe it's my own issues, but going to religious sites, particularly in the US, is often pretty uncomfortable for me. The Mormon Temple in Salt Lake is always bad, and even with historic churches, I feel like I shouldn't be there. They feel cold to me.
The Baha'i Temple, just north of the city in the quiet, wealthy, lakeside suburb of Wilmette, was not like that for me. It's peaceful, quiet and gave the impression that I was free to explore at my own pace and not have to worry about being bothered by someone trying to tell me about the faith.
It's nice too because it's totally free, and it's easily accessible by public transit.
A trip to Wilmette is usually on my list of things to do when I visit Chicago, because of the nice beach facilities they have, the wonderful and stately homes, and this temple.