Known as the Moonlight Sonata, this work breaks from traditional Classical forms by beginning with an ethereal, dream-like movement. Its haunting atmosphere and sustained pedal effects pushed the boundaries of early 19th-century keyboard writing.
The performer must achieve a perfectly even, delicate balance between the triplet accompaniment and the primary melody.
Comparable difficulty and character — good candidates for what to learn next.
Piano Sonata No. 14 'Moonlight', No. 2 is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 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 Piano Sonata No. 14 'Moonlight', No. 2 lasts about 15 minutes.
Piano Sonata No. 14 'Moonlight', No. 2 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 Piano Sonata No. 8 'Pathétique' by Ludwig van Beethoven, Andante favori by Ludwig van Beethoven, Piano Sonata No. 17 'Tempest', No. 2 by Ludwig van Beethoven — see the full similar-pieces list on this page.