I have visited MOCRA many times and have always found inspiration, either mental or spiritual. Their exhibits are sometimes awe-inspiring, not always classically beautiful, but definitely worth the time spent. It's on the campus of St. Louis University and relatively easy to find. You should check their website or Facebook page for information about current exhibits.
This museum is small, but thought provoking. It led to some good conversations about people's views on religion. It probably took under an hour to see the museum. The most time consuming part was finding parking, since the spots near the museum were already taken.