Cooman's 'Fantasia pro organo pleno' is a majestic and energetic piece for the organ's full chorus. You'll hear the majestic atmosphere in the 'molto grave' parts. The energetic (and almost ecstatic) allegro parts never lose their majestic feel.
It is the second fantasia of the bundel 'Two Fantasias'.
Carson kindly allowed to use some snippets of the score in the video. So you can have an idea of the score.