Discuss and learn French: French vocabulary, French grammar, French culture etc.
"Cela va être une excursion manifique" or "Cela (or ce ) sera une excursion manifique" I think.
Hi Janek -- Just to expand slightly on what George has already said:
Your sentence "La excursion va être magnifique" is of course fine. As you can see, the complication comes when you need a pronoun (equivalent of "it") at the start of the sentence.
When choosing between "C'est..." vs "Il/elle est..." to mean "It's...", then as a rule of thumb, "C'est..." is strongly favoured when followed by a noun or noun phrase. So in this case, "Elle va etre..." is essentially ruled out unless by "Elle" you actually meant "She" referring to a person.
Then, the other complication is that ce/c' is used as the subject of être when it is just être that is present. Nowadays, whenever you get some other auxiliary used with être, then speakers generally use ça/cela instead. So:
C'est..., Ce sera..., Ce sont..., Ce seraient... etc
But: Ça doit être..., Ça va être..., Ça a dû être...,
(In older literature, you will find "ce doit être..." etc, but nowadays it's essentially old-fashioned or at least extremely formal.)
Hopefully that helps, but let us know if you want further explanation!