Get out the microscope, because we’re going through this poem line-by-line.
By a route obscure and lonely,
Haunted by ill angels only,
Where an Eidolon, named NIGHT,
On a black throne reigns upright,
- This is a refrain (a repeated set of lines, like a chorus in a song) that's exactly the same as the four opening lines of the poem. This gives the whole thing some nice balance, and it also makes the repeated images (like the Eidolon) stick in our heads.
I have wandered home but newly
From this ultimate dim Thule.
- The twist here is that now the speaker isn't coming to Dream-Land, he's leaving. Now he has "wandered" home again. Given what he's said about Dream-Land being Eldorado, we're not sure if leaving it is something to be happy about.
- Notice that this is one of only two times in the poem (the other being line 5) where the speaker refers to himself directly, using the word "I." This makes these two lines, the beginning and end of this mysterious journey, even more gripping.