what is the source of the endless fountain of immortal drink?

According to Keats, nature has always been a source of perennial beauty. The beauty of nature can be found in heavenly bodies like the sun and the moon, in natural objects like trees and sprouting shrubs, even in a simple animal like the sheep and flowers like the daffodils and musk-rose. These are beautiful things which have the capacity to ease our pain. Apart from natural objects, the poet also finds beauty in the death of martyrs who have laid down their lives for a noble cause. The lovely tales of these brave souls tell us hope is still there.