A brief interlude in the home of Tom Bombadil.
Elements of this stay remind me of the stay with Beorn in The Hobbit, particularly considering the nature-druid spin they gave him in the film adaptation. The Old Forest is not a place where our hobbits expected to find friends or friendly shelter, yet they find true sanctuary in Bombadil's home. Other elements remind me of various interactions with elves, but with less artifice. The elves often use song and merriment to hide their nature and power. For Tom, song is much a part of him as breathing.
Tom himself refuses to be defined, but exists outside of time, predating even the elves. The fact that the Ring has no effect on him is remarkable. Even the Istari have something to fear from the Ring's influence. Perhaps the lack of effect is related to his position as a Master with great power, but without any ownership.
"He is, as you have seen him," she said in answer to his look. "He is Master of wood, water, and hill."
"Then all this strange land belongs to him?"
"No, indeed!" she answered, and her smile faded. "That would indeed be a burden."
However, for all his power, the sanctuary of his home is not absolute. The hobbits' dreams are touched by something outside themselves.
Tom may be largely untouched by the darkness of the world at large... but I don't think Goldberry is. She understands fear and danger. Tom knows about the darkness, but it doesn't really touch him. Again, I also think that Merry and Pippin have a better grasp on what they're facing than Frodo does. I don't think it's just remembered fear of their encounter that makes them cry out to not speak of Old Man Willow at night.