Finally a topic I can really contribute to! The Underground is located at Adventureland in Des Moines, Iowa (my backyard). I went on this ride a couple of times during my annual trip down to the state capital's park. Let me first say that this ride is awesome for trying to escape a hot day as the ride features a couple of spots where you get lightly sprayed with water (at least I hope that was water) Its got a couple of chain lifts, but no drops.
The ride isn't much in terms of thrills, and it features some pretty corney wooden models of a mine camp and Adventureland's "Outlaw"* who has hidden out in the ride.
Like I said its fun to beat the heat on, and the line moves pretty fast, but it doesn't pack a lot of punch in the thrill-o-meter.
* The Outlaw is also the name sake of one of CCI's first coasters also located at Adventureland. Great woodie.
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Randy Hutchinson
You build it, I'll ride it