This likely refers to the famous Aria from Bachianas Brasileiras No. 5, often transcribed for piano. It's a deeply evocative work that merges Bach's contrapuntal spirit with Brazilian folk song, creating a lush, singing texture.
Achieving a seamless, singing legato melody and a rich, resonant tone through careful pedaling and voicing is paramount.
Bachianas Brasileiras No.5, W.389 is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
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.
Bachianas Brasileiras No.5, W.389 is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.