The speaker reads a caption about an Italian beach where men aren't allowed, so women can swim and sunbathe without cat-calls or stares. That night he dreams of an endangered sea turtle who has just buried her eggs and then rises from the sand in the shape of a woman. His closing thought, "So that's what they do / when we're not around," is the poem's small punchline.
The tone is light and a little wry, but there's something more thoughtful underneath. The speaker seems curious rather than resentful, almost like someone peeking at a secret. Yet the dream shows how little he actually knows: he can only picture women's private lives through a strange, half-magical image. The turtle suggests vulnerability, since she is endangered, and also care and quiet strength, since she has just protected her eggs. The mood is gentle and dreamlike, with a hint of self-awareness that his own presence is usually the thing women need a refuge from.