Čiurlionis's Basso Ostinato is a masterful study in recurring thematic material layered against complex, chromatic accompaniment. Its dark, insistent character makes it a unique contribution to early 20th-century piano literature.
Maintain absolute rhythmic regularity in the ostinato figure while layering the upper voices expressively.
Comparable difficulty and character — good candidates for what to learn next.
Basso Ostinato, VL 267 is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 8.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 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 Basso Ostinato, VL 267 lasts about 5 minutes.
Basso Ostinato, VL 267 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 Canon in C minor, VL 216 by Mikalojus Konstantinas Čiurlionis, "Oh Woods("Oi giria, giria"), VL 276 by Mikalojus Konstantinas Čiurlionis, Canon in A major, VL 116 by Mikalojus Konstantinas Čiurlionis — see the full similar-pieces list on this page.