We've had lots of fun with this question amonst ourselves. Though never said outloud, some of the possible answers we considered were:

1) Concrete ginger bread man (pre-inflation)
2) New city lift station
3) Hog facility (pre-windows)
4) Meeting center for former arctic dwellers.
5) Church of Living Round

Ultimately, after hearing the question enough, we decided it was time to be proactive -- and put the real answer on a printed hand out. In a few words, it captures the many benefits of a Monolithic Dome. Here's what it says:

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Trinity Dome - Vermillion, South Dakota - Page Generated in 0.0528 seconds