The poem's speaker will find peace for himself on the isle (small island) of Innisfree, which is in the middle of a lake. He will build a small cabin there, where he will live alone, plant nine rows of beans, and keep bees. He will feel peace there from morning to midnight because he will be immersed in enjoying the beauties and quiet of nature.

As for the "when," he says that he will go there "now." This, along with the rest of the last stanza, indicates that the lake isle of Innisfree is a dreamscape that he retreats too whenever he feels stressed out. He says he can hear the lapping of the water in his heart all the time, even when he is standing on a busy urban sidewalk ("pavement").

It is what we today might call our "happy place," the mental refuge we enter when life seems overwhelming.