Millennium Force. It's so incredibly breathtaking. The smooth drop down into the overbanked turn is nothing short of awesome, especially from the causeway... and that's during the day. At night, that sucker lights up to be one of the most surreal, astonishing, and beautiful manmade things I've ever seen. Hell, to me it tops some of the natural wonders I've seen.
Mean Streak is also a pretty ride, but Shivering Timbers, although it's not the cleanest looking coaster, nor is it in the best setting, it's just so easy on the eyes. Especially when you're sitting in the parking lot watching a train run the whole circuit.
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How dare you vanquish the Steel Phantom without his consent? Fear the Phantom's Revenge.