Let's take a look at the definition of adjective and adverb as a start. (According to Cambridge Dictionary)
Adjectives are words that a word that describes a noun or pronoun.
Adverbs are a word that describes or gives more information about a verb, adjective, adverb, or phrase.
In this case,refreshing is used to describe the bike trail. Therefore, it is an adjective.
Hope it helps!
