Inverted: To the east of the building is the car park.
Someone said my sentence was wrong. I want to explain to her that the sentence is inverted. I put the bold part ahead. Is the bold part called the adverbial? I put the adverbial ahead and therefore the verb should also be put ahead.
Normal: the car park is to the east of the building.
The bold phrase is a prepositional phrase, with "to" as its head. In that sentence, it has an adverbial function, so yes, it's an adverbial.
A simple test is to see what question the phrase answers. If it answers a "what" or "who" question, it's probably a noun phrase. But if it answers a "when", "where", "why" or "how" question, it's an adverbial. In this case, the question is "where", so the phrase is adverbial.
When we're talking about parts of a sentence, we should refer to phrase types rather than functions, so "I put the prepositional phrase ahead..." is a more accurate way to phrase it.