They crossed the moat
This castle almost perfectly fits the description of the castle Christabel and her family reside. There is a moat and if you look closely you can see a what looks like an iron gate. The castle pictured is also surrounded by a wooded area much like the castle described in this poem.
Tu—whit! Tu—whoo!
In the nineteenth century many poets used owls to represent a bad omen. They refereed to the owl as the "bird of doom." So, here we can see Coleridge warning us that the plot is headed somewhere dark.
Quoth Christabel, So let it be! And as the lady bade, did she. Her gentle limbs did she undress, And lay down in her loveliness.
Christabel is a symbol of purity and devoutness. She is very christ-like. While Gerdaline seems to be symbolic for sexuality and sin. Christabel is constantly praying throughout the poem whereas Gerdaline is asking Christabel to undress herself to cast a curse on her.
Langdale Pike
Langdale Pike is a group of peaks in the Lake District (England).
With white-flowered jasmin, and the broad-leaved myrtle,5(Meet emblems they of Innocence and Love!)6And watch the clouds, that late were rich with light,
According to Oxford dictionary the word "jasmin" means a shrub that bears white, pink, purple flowers. The word "myrtle" is an evergreen shrub with white flowers and oval shaped berries.
My pensive Sara! thy soft cheek reclined2Thus on mine arm, most soothing sweet it is3To sit beside our cot, our cot o'ergrown
Coleridge is referring to his wife Sara, whom he married shortly after writing this poem. Her cheek is resting against his arm and it is soothing to him as they side on their cot. According to Oxford dictionary the word "cot" means bed.
8Just at sun-set, when thrushes sing, 9I saw her dash with rapid wing, 10And hail’d her as she pass’d.
According to the Oxford dictionary, "thrushes" means a medium-sized song bird. Smith is saying just as the sun sets the song-bird/thrush sings. She says she saw the bird with her rapid wings. The words rapid and dash implies that the bird was flying with control and great control.
1Come, summer visitant, attach 12To my reed roof your nest of clay, 13And let my ear your music catch 14Low twittering underneath the thatch 15At the gray dawn of day.
According to Oxford dictionary, the word "reed" means a tall slender leaved-plant that grows in water. Smith is referring to the the swallow (a migratory bird) as the summer visitant. She tells the swallow to attach to the tall plant where perhaps the swallow's nest rests. She goes on to say that she would like to her the music the bird is making.