This suite is considered one of the most virtuosic and challenging works in the entire piano repertoire, based on poems by Aloysius Bertrand. It is distinguished by its incredible range of tonal colors and extreme technical demands.
Mastering the control of ultra-fast repeated notes in 'Scarbo' and maintaining atmosphere through intense technical strain are the primary hurdles.
Comparable difficulty and character — good candidates for what to learn next.
Gaspard de la nuit 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 Gaspard de la nuit lasts about 23 minutes.
Gaspard de la nuit 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 Jeux d'eau by Maurice Ravel, Miroirs by Maurice Ravel, Hungarian Rhapsody No. 2 in C-sharp minor by Franz Liszt — see the full similar-pieces list on this page.