In a not so distant future where overpopulation has become a big problem for the government, the cities started growing and growing. Space for rollercoasters was scarce, so companies had to get inventive with their location for their park.
Skyscrapers, power line towers and all sorts of buildings were partially repurposed for their dreams. Noise complaints, you say? Yeah, let's not talk about that.

(Please use cut-away view to inspect the plot as a big part is underground)