Posting here for reference.
It is possible to enter into Skyscraper without unlocking it. See Vorpal highlight who discovered this: http://www.twitch.tv/vopeju/c/4063680
Basically, entering and exiting twice the first level of a warp zone places you to the first stage of the world. If there is a warp zone on that stage, it places you on the warp. Then you can enter it.
Also, if you enter/exit twice the second (resp. third) level of a warp, it places you on the second (resp. third) stage of the world.
It is possible to enter into Skyscraper without unlocking it. See Vorpal highlight who discovered this: http://www.twitch.tv/vopeju/c/4063680
Basically, entering and exiting twice the first level of a warp zone places you to the first stage of the world. If there is a warp zone on that stage, it places you on the warp. Then you can enter it.
Also, if you enter/exit twice the second (resp. third) level of a warp, it places you on the second (resp. third) stage of the world.