In which poetic work does "A thing of beauty is a joy forever" appear?

The phrase "A thing of beauty is a joy forever" appears in John Keats' poem "Endymion." This work is a narrative poem that reflects on themes of beauty, love, and the transcendental nature of the ideal. Keats emphasizes the enduring nature of beauty, suggesting that it offers ongoing joy and solace to those who appreciate it, which is encapsulated in this line. The poem itself was influenced by classical mythology, particularly the story of Endymion, a shepherd who falls in love with the moon goddess Selene, reinforcing the connection between beauty and divine love.

In contrast, "Hyperion," "The Prelude," and "Ode to a Nightingale" are notable works by other poets or deal with different themes and structures that do not contain that specific line. "Hyperion," also by Keats, explores the theme of change and the fall of the Titans, while "The Prelude," written by Wordsworth, is an autobiographical exploration of the poet's development, and "Ode to a Nightingale" meditates on mortality and the ephemeral nature of beauty and life. None of these encapsulate the same sentiment as expressed in "Endymion."