Goethe in Marienbad - the Marienbad Elegy
Goethe visited Marianske Lazne (what was then Marienbad) first in 1820, and then in several summers. In 1821, he met Ulrike von Levetzow. Goethe was 72 at that time and von Levetzow was 17. He immediately fell in love with the girl and two years later dared to do the impossible. With the help of a friend he proposed to Ulrike! More or less logically, she didn't feel like him and rejected the proposal. Later she stated that she "loved him just like a father", but not more. Goethe became really depressed when he heard about the rejection and suffered so much that he tried to compensate his suffering in writing. On his way home, he started writing the "Marienbad Elegy" in which he mourns the loss of Ulrike's love. See this link for a complete version of the elegy. Nowadays, the elegy counts as one of Goethe's main works, regarded by some as his most personal poem.
Interestingly, Ulrike von Levetzow became very important in humanist studies later. She lived until the biblical age of 95 and thus was at the end of her life (1804-1899) the only person who had met Goethe!