One of the eight types of adverb, showing location.
“He is staying there.” “She is working in the barn.” “They will go where they wish.” There is a single adverb of place. In the barn is an adverb phrase of place. Where they wish is an adverb clause of place.
Such words as home and today are usually, but not invariably, nouns. In such sentences as “Today I went home”, they are in fact adverbs.