This poem, set in a prison, is most known for its lines: "Stone Walls do not a Prison make,/Nor Iron bars a Cage." A very brief synopsis is that imprisonment is a state of mind. In this poem, the speaker can escape the drudgeries of prison life by imagining that his lover Althea is there to see him.

The author, Richard Lovelace, might know, as he spent time in jail essentially for speaking his mind during a political period in England when it was not wise to do so. 

To Althea, from Prison

BY RICHARD LOVELACE

When Love with unconfinèd wings

   Hovers within my Gates,

And my divine Althea brings

   To whisper at the Grates;

When I lie tangled in her hair,

   And fettered to her eye,

The Gods that wanton in the Air,

   Know no such Liberty.

When flowing Cups run swiftly round

   With no allaying Thames,

Our careless heads with Roses bound,

   Our hearts with Loyal Flames;

When thirsty grief in Wine we steep,

   When Healths and draughts go free,

Fishes that tipple in the Deep

   Know no such Liberty.

When (like committed linnets) I

   With shriller throat shall sing

The sweetness, Mercy, Majesty,

   And glories of my King;

When I shall voice aloud how good

   He is, how Great should be,

Enlargèd Winds, that curl the Flood,

   Know no such Liberty.

Stone Walls do not a Prison make,

   Nor Iron bars a Cage;

Minds innocent and quiet take

   That for an Hermitage.

If I have freedom in my Love,

   And in my soul am free,

Angels alone that soar above,

   Enjoy such Liberty.