Where is William famous painting the harp that once?

You're likely referring to the painting "The Harp That Once Through Tara's Halls" by William Butler Yeats, not a famous painting. It's not a visual artwork, but a poem!

The poem itself isn't "located" anywhere physically, but it is widely known and studied in the world of literature. It's considered a classic of Irish poetry, and it's often featured in anthologies and textbooks.

Would you like to know more about the poem "The Harp That Once Through Tara's Halls"?