The space shuttle was huge and marvelous.
The problem with the original sentence is that it's trying to use a noun and an adjective to describe the space shuttle. To make it parallel, you need to make both descriptors nouns ... or both adjectives, as I've done above.
Is this a parallel sentence? If so how can it be written more simpler.
The space shuttle was both a marvel and huge.
2 answers
The space shuttle was both a marvel and huge.