In Percy Bysshe Shelley's "The Triumph of Life," there are several similes used.
Around line 290, Shelley writes about the Church rising "like shadows" between man and God. I take this to mean that Shelley feels that instead of drawing mankind closer to God, the Church, specifically Pope Gregory the Great, is acting more like an obstruction.
The recurring theme here seems to speak to the conflicts organized religion (Christianity) has created that separates mankind from God.
Then there is a shift at approximately line 314: Shelley is describing the coming of spring; the speaker notes he had fallen asleep under a mountain as the world outside comes to life. He was in a "cavern deep," there for an immeasurable time, and...
...from it came a gentle rivulet / Whose water like clear air in its calm sweep...
This simile draws attention to the beauty of all that is natural, that surrounds him, but there is a sense of the mystical: we find this in...
I found myself asleep
Under a mountain, which from unknown time
Had yawned into a cavern high and deep
We see it again with the following:
And from it came a gentle rivulet
Whose water like clear air in its calm sweep 315
“Bent the soft grass and kept for ever wet /
The stems of the sweet flowers, and filled the grove
With sound which all who hear must needs forget...
The sense of the "supernatural" (not in sense of ghosts, etc., but things beyond the "natural world") would have been anything but unusual in the poetry of Shelley, one of the three great second-generation Romantic poets in English literature.
In this mystical place, Shelley describes the water "like clear air," and sounds like an allusion to Greek Mythology and the the River Lethe:
...it was believed that the newly dead who drank from the River Lethe would lose all memory of their past existence.
So that the water in the poem, like the sweet air Shelley describes:
With sound which all who hear must needs forget
“All pleasure and all pain, all hate and love, Which they had known before that hour of rest: 320
A sleeping mother then would dream not of
“The only child who died upon her breast At eventide, a king would mourn no more
The crown of which his brow was dispossest...
Shelley describes that this water would remove all memory previous, and this included the memory a mother would have of losing her only baby, but would also comfort the king who had lost his crown and kingdom.