This refers to an opera by Schubert, likely a specific aria or orchestral excerpt arranged for piano, known for its dramatic scope and lyrical beauty.
The primary technical challenge is managing the dramatic contrasts and maintaining a rich, resonant tone throughout the expansive melodic lines.
Alfonso and Estrella (D.732) 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 Alfonso and Estrella (D.732) lasts about 15 minutes.
Alfonso and Estrella (D.732) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.