"A skyscraper of Korea"
Okay so im pretty sure 마천루 isnt incorrect,, but as far as im concerned, its more of an idiomatic expression-- like i have literally never heard any actual korean person say that, they all say 고층건물 or 초고층건물
Pronunciation-wise, the app said (마철루). I thought I remember learning that it would be pronounced (마천누). Which is it?