In the spring of 1834, Chopin attended the Lower Rhenish Music Festival in Aix-la-Chapelle with Hiller, and it was there that Chopin met Felix Mendelssohn. After the festival, the three visited Düsseldorf, where Mendelssohn had been appointed musical director. They spent what Mendelssohn described as "a very agreeable day", playing and discussing music at his piano, and met Friedrich Wilhelm Schadow, director of the Academy of Art, and some of his eminent pupils such as Lessing, Bendemann, Hildebrandt and Sohn. In 1835 Chopin went to Carlsbad, where he spent time with his parents; it was the last time he would see them. On his way back to Paris, he met old friends from Warsaw, the Wodzińskis. He had made the acquaintance of their daughter Maria in Poland five years earlier, when she was eleven. This meeting prompted him to stay for two weeks in Dresden, when he had previously intended to return to Paris via Leipzig. The sixteen-year-old girl's portrait of the composer is considered, along with Delacroix's, as among Chopin's best likenesses. In October he finally reached Leipzig, where he met Schumann, Clara Wieck and Felix Mendelssohn, who organised for him a performance of his own oratorio St. Paul, and who considered him "a perfect musician". In July 1836 Chopin travelled to Marienbad and Dresden to be with the Wodziński family, and in September he proposed to Maria, whose mother Countess Wodzińska approved in principle. Chopin went on to Leipzig, where he presented Schumann with his G minor Ballade. At the end of 1836 he sent Maria an album in which his sister Ludwika had inscribed seven of his songs, and his 1835 Nocturne in C-sharp minor, Op. 27, No. 1. The anodyne thanks he received from Maria proved to be the last letter he was to have from her.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): Where did Chopin meet Felix Mendelssohn?
the Lower Rhenish Music Festival