This monumental work by Busoni is a profound tribute to Bach's Art of Fugue, expanded through a massive, late-Romantic and early-Modern harmonic lens. Its distinctiveness lies in its combination of archaic contrapuntal rigor with the most advanced keyboard demands of the early 20th century.
At Henle 9 this is among the most demanding works in the piano literature. The main demands: independent voices that must each sing on their own line; big chords that need weight without harshness; and fine finger independence within the hand.
Beyond that, expect polyrhythms that have to lock together without sounding mechanical, and chord voicing — bringing out one note inside a handful of others.
At roughly 25 minutes, stamina and memory become part of the challenge — plan practice in sections.
The immense challenge is the architectural management of complex, multi-layered contrapuntal voices requiring extreme finger independence.
Comparable difficulty and character — good candidates for what to learn next.
A level or two down with the same spirit — ideal if this piece is still out of reach.
Lesser-known works by the same hand, at a comparable level.
Fantasia Contrappuntistica, BV 256 is rated Henle level 9 of 9 — virtuoso repertoire, roughly concert / virtuoso level. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 9 — meaning you can already play level 8–9 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Fantasia Contrappuntistica, BV 256 lasts about 25 minutes.
Fantasia Contrappuntistica, BV 256 is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Fantasia contrappuntistica by Ferruccio Busoni, Fantasia Contrappuntistica, KiV 256 by Ferruccio Busoni, Canonic Variations & Fugue in C Minor by Ferruccio Busoni — see the full similar-pieces list on this page.