The thing that the poet finds so attractive about Lake Isle of Innisfree is its promise of peace:
And I shall have some peace there, for peace comes dropping slow,
Dropping from the veils of the morning to where the cricket sings,
There midnight's all a-glimmer, and noon a purple glow,
And evening full of the linnet's wings.
The poet, then, longs for this place which affords a sense of contentment and relaxation far from the busy modern world. Note how the poem's slow and regular meter helps to convey this languid, dreamy effect. There is also the vivid impressionistic description of the colours and beauties of this place, and the soothing stir of nature which is so different from the strident noise of the city where the poet actually is, as the final stanza makes clear.
The poet, then, is physically trapped in the city, but he can imagine the beauty of Innisfree and this gives him spiritual sustenance. This is one of Yeats's early lyrics, exhibiting a familiar romantic sensibility in its praise of the deep purity and beauty of nature which is contrasted with the drabness, shallowness and sterility of modern urban living.