Which is the difference between:
"What a beautiful day" and "Such a beautiful day"?
However, "Such a beautiful day", whilst probably said quite regularly, shouldn't actually be the whole sentence - it should be "It is such a beautiful day". It could in fact be followed by something else related to the fact, for example "It is such a beautiful day that I'm going to go for a long walk in the mountains!".
In their basic meaning of course, they are the same, you are simply commenting on the fact that it is a very beautiful day!