You're absolutely right about St. Louis Cathedral Basilica, words (and pictures) can't describe it, you've just got to see the interior to properly appreciate it.
Not trying to turn this in to a mormon temples thread, but I'm mormon, so its what I'm most familiar with. Plus, there are a lot of them around the world, and they tend generally to have pretty unique architecture. These are a few of my favorites that may qualify as 'badass':
Ogden, Utah:
Mexico City:
Portland, OR:
Las Vegas, NV:
Manti, UT:
Cardston, AB:
For all of the interesting ones though, there are about 50 around the world that all look exactly the same as this one in Spokane, WA:
(all images via
www.ldschurchtemples.com)