"Spellbound" begins on a dark and stormy night that's only getting darker. This is no evening to be out in the weather, but this speaker, caught in the storm, can't stir a foot to escape. A "tyrant spell," they declare, has "bound" them, so that no matter what, they "cannot, cannot go." Readers are left with the image of some poor soul marooned in a chilly night, frozen on the spot—straining to move and unable to stir.
The whooshing alliteration of "wild winds" and the round, mournful assonance of "coldly blow" echo the howling of those winds, bringing the eerie scene to life. Note, too, how the rhythm here and throughout the poem echoes that of a nursery rhyme—three-beat accentual meter, lines that use three regular strong stresses but don't stick to any one kind of metrical foot. Take lines 1-2:
The night is darkening round me,
The wild winds coldly blow;
These rhythms, combined with the use of plain, straightforward language, only deepen the poem's strangeness and sense of mystery. The merciless spell that holds the speaker here seems to have come out of nowhere. Personified as a "tyrant," a cruel ruler, perhaps it cast itself. Why the spell persecutes the speaker, however, isn't clear. All readers can know is that it leaves the speaker in despair. The helpless, insistent epizeuxis of "I cannot, cannot go" suggests that this poor speaker has tried and failed to stir from the place they're stuck. But all they can do is stand still and watch as the world grows darker and colder and more dangerous all around them.