WordNet sense 1 (someone who believes in the existence of realities beyond human comprehension):

religious mystic

WordNet sense 2 (relating to or resembling mysticism):

mystical

WordNet sense 3 (having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding):

mysterious, occult, secret, orphic

WordNet sense 4 (confined to and understandable by only an enlightened inner circle):

esoteric