Bach was particularly admired for his keyboard skills, not least his knack for improvisation; much of his organ music probably started out life as just that – a doodle turned into something mighty. Leaving aside the most famous organ work of all, the Toccata and Fugue in D minor (which some doubt is by Bach at all), one of the most brilliant works is his Fantasia and Fugue in G minor. The free-flowing Fantasia has an angular beauty and a dark-hued mood that comes from Bach's liking for crunchy dissonance, while the Fugue is a tour de force that builds to a firmament-shaking climax.