Intensifying with "duo"

多 in an exclamation means "how…!" — the same word that asks about degree.

多 + Adj. (+ 啊)

How it works

多好！ — how wonderful! 外面多舒服！ — how pleasant it is outside! Often finished with 啊.

This is the statement counterpart of the question 多高?. Intonation and context tell them apart.

多么 is the fuller, more literary form: 多么美丽的城市.