I am deathly afraid of roller coasters; the biggest I have ever been on was in Santa's Village in Bracebridge. They also seem to be a waste of energy, pulling those cars up a fake metal hill just to have them fly down the other side, what's the point? Some people prefer to cycle or walk, and now they can, on a walking roller coaster. I think I might be able to handle Tiger and Turtle - Magic Mountain” by Heike Mutter and Ulrich Genth in Duisburg.
It is 21 meters (69 feet) high, although I am not quite sure how you do that top loop.
The designers describe it:
The curved flight of stairs inscribes like a signature on the landscape and recruits the nimbus of the classical roller coaster. Having a closer look, the public is disappointed in a disarming way. The visitor climbs on foot via differently steep steps the roller-coaster-sculpture. So the sculpture subtly and ironically plays with the dialectic of promise and disappointment, mobility and standstill. Visitors happen to briefly meet with oncoming visitors on the steep and about 1m (3') wide corridors.
There are LEDs embedded in the handrails to make it accessible at night, and beautiful to look at.
It is on a built-up "magic mountain" and provides an impressive view of the Rhine. More at Heike Mutter & Ulrich Genth
And if you don't want to walk, there is always the TreeHugger-Style Roller Coaster in Japan: It's Pedal Powered.