A widow's walk is the railed platform on a coastal house where, traditionally, people watched the sea for ships. Here it becomes a place of looking back and wanting. The speaker begins with a question: who is fit to go to sea "in the heart"? The sea turns into an image for deep feeling, for the risk of loving or longing, and the speaker doubts anyone is truly ready for it.
The middle lines reach toward "some other weather," something the speaker aches to sense but can't quite touch. Then comes a plain, tired admission: "but I am old." The poem ends with a blunt statement that the pretty girl who sang and danced is dead. It's unclear whether this means a lost loved one or the speaker's own younger self, and the poem seems to hold both possibilities. The mood is quiet, wistful and grieving, with short lines that leave a lot of empty space, like the stretch of water the speaker keeps staring across.