The speaker of "Splendour Falls" is alone in the mountains, looking across the valley at sunset and describing the scene. It's gorgeous, but there is something about this particular scene of nature that is especially evocative. It reminds the speaker of fairy tales, of the past, of ancient history and mythology, and eventually of our lives' legacies after death. Woah. That's a lot of power, even for a beautiful valley!
Put your thinking caps on. In "The Splendour Falls," the grandeur of nature makes the speaker think about major, capital-letter ideas like Philosophy, History, Mythology, and the Future.
The incredible shrinking speaker—the distance across the valley in "The Splendour Falls" makes the speaker feel suddenly tiny and insignificant in the scope of history.
"The Splendour Falls on Castle Walls" is partly a description of a beautiful scene in the mountains and the speaker's response to the echoes of a bugle. Listening to those echoes, though, makes the speaker reflect on different kinds of "echoes." What kind of "echo" has the past left on the present? Does ancient mythology leave a kind of "echo" in the modern era? And—perhaps most importantly for our speaker—what kind of an "echo" will we leave behind us when we're gone… gone… gone…? (See what we did there?)
Ready for a downer? The various kinds of sound "echoes" in the poem (alliteration, internal rhyme, end rhyme, repetition) help to emphasize the poet's anxiety that all of his poetry is only empty noise and sound, like an echo.
Think the past is over and done? Nope. The "echoes" described in the poem are the literal version of the kind of figurative echoes that the past can have on the present.
The speaker of "The Splendour Falls on Castle Walls" is walking in the hills above a castle—alone. Does that bum him out? Not one little bit. He watches the sunset, takes in the beautiful scenery, and enjoys the solitude. Suddenly, though, he hears a bugle horn that seems to come out of nowhere. He's not as solitary as he thought he was! But the combination of his apparent isolation, with the reminder of other people (that he can't see), contribute to the kind of deep thinking and reflection that he's able to accomplish here.
Although the speaker of "The Splendour Falls" seems to be completely alone, the sound of the bugles reminds him abruptly that solitude is only ever an illusion. Every corner of the earth, even if uninhabited today, is still inhabited by the "echoes" of historical men and women. You can't get away!
Bugler? What bugler? The speaker of the poem addresses the bugle, instead of the person playing it, in order to sustain the illusion of solitude and of being isolated from other people.
The theme of "Immortality" is pretty closely related to "Memory and the Past" in "The Splendour Falls on Castle Walls": both have to do with the ways that "echoes" can affect us. But instead of the "echoes" of the past coming back to haunt us in the present, the speaker realizes at the end of the poem that we create "echoes" of our own that can give us a kind of immortality. That's not so bad, right?
Tennyson forever! The reference to fairy tales and mythology through the description of the "castle" (1) and the mention of "Elfland" (10) suggest that literature can offer a kind of "immortality," which suggests that the poet was consciously trying to attain this kind of literary immortality for himself.
Immorality is like an exclusive club. The "echoes" of line 14 serve as a kind of conduit for immortality, but it is an immortality that is only available for people who understand the deep connection between individuals that the speaker has realized.