Can you write a sentence with that phrase as the subject? Perhaps the site was carefully selected by a committee. Perhaps it's under 3 feet of water because of a flood. Try writing a sentence using it as the subject and you will have fulfilled the first requirement.
Then see if you can come up with something on your own for the other part of you question.
I learnt that in an structure like " where the competition was held is far", the underline part is performing a nominal function in the sentence, thus, it is functioning as a subject in the sentence. Again, in a sentence like "where the competition was held, i can't tell." the same structure is performing an adverbial function. Thus, it is functioning as an adverbial clause of place