You have NO IDEA how much time in my physics lessons is devoted to daydreaming about this precise topic!
I haven't really got a 'park' I'd make, I got a few ideas for rides though -
Cliffhanger - Literally, a cliff hanger, this stupidly tall drop tower would have its main winch at the top of a cliff, and have cables run to the base of the cliff, stretched with enough tension so they stay straight, and that would be used to hold the car on - so saving much weight on building a freestanding tower.
The ride would be the height of the cliff, plus about 50 ft, as the supports would be built like a crane, with a 45* beam held up over the cliff by a cable running down at a gentler angle from the apex. It would be winched up, and winched back down again at a rate slightly faster than freefall, and also stopped by the same winch.
Black hole - A Vertical flume ride, unlike the 'vertical' flume rides around now, this one would actually be vertical. You would step onto a platform, with a bar above you. The platform would then drop away to the sides, revealing a 20m vertical drop into blackness before an extended pullout, and then a flat section of clear tunnel that goes underneath the water level of the main pool, so swimmers can watch you shoot through the tube.
There would also be a bar above the platform, so that if you were strong enough and wanted to, you could just 'hang' over the drop, for a few seconds, after the platform dropped away.
Mega fun coaster (final destination style) - An evilly themed coaster, this coaster would be probably a eurofighter. The track and trains would be coloured a faded, but sickly green, or another bright fairground colour. The theming would be seemingly nonexistent, apart from a large, chipboard tower over the top of the lift hill, and high barbed wire fences around the area.
The ride layout would be fairly unremarkable - at the least, it would have a vertical lift and a loop, for reasons I will explain. On the vertical lift, the coaster would reach almost the top, make a loud clanking noise, and fall back down about 40ft of lift hill, before being caught, and resuming the climb up the lift hill. On the loop, the train would seem to stop at the top of the loop, to be guided slowly round the top by inconspicuous friction wheels. At the very top of the loop, the restraints would suddenly vibrate, giving the impression that they had come undone slightly (of course, they'd only have rattled a bit). And finally, on the brakerun, the train would overshoot the first brakerun, only to come to a stop inches before hitting the train in front.
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Well, I would go on, but I plan to design rides in the future, and if I give all my ideas away now, I'll have none left for when I get a job!
Plus, I doubt most people will bother to read all of that