Magnificent, Grand, Epic
noun, な adjective
It's so robust and big! Things like this are magnificent, grand, and epic!
そうだい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
なんて壮大な曲なんだ。凄く感動しています。
This is such a magnificent song. I’m so impressed.