“The sky was pure, flat gold like the background of a medieval picture. The ocean was gold too, in the offing, flecked with innumerable shadows. The nearer waves, though golden where their summits caught the light, were green on their slopes: first emerald, and lower down a lustrous bottle green, deepening to blue where they passed beneath the shadow of other waves.… Far below him in a vast, momentary valley he saw the thing that had missed him. It was an irregularly shaped object with many curves and re-entrants. It was variegated in colour like a patch-work quilt-flame colour, ultramarine, crimson, orange, gamboge, and violet. It sat to the water like a skin, curving as the water curved. It took the wave's shape at the top, so that for a moment half of it was already out of sight beyond the ridge and the other half still lying on the higher slope. This thing might have been thirty acres or more in area.… And that is the nature of the floating islands of Perelandra.”
—Perelandra, Chapter 3 by C.S. Lewis

Not more than one person in five hundred years finds this tiny island. It doesn't stay in one place very long. But anyone who is drawn to these mysterious lanterns, and comes to get a closer look, vanishes into another world, and never comes back. The question is, do they want to?

Frodo and his friends are leaving the Shire secretly by going west into the Old Forest, instead of north to the road. The Forest is reached through a break in the Hedge used to keep the unfriendly trees out of the Shire …

“It had walls of brick at the sides, which rose steadily, until suddenly they arched over and formed a tunnel that dived deep under the Hedge and came out in the hollow on the other side.

“It was dark and damp. At the far end it was closed by a gate of thick-set iron bars. On the far side was a faint path leading up on to the floor of the Forest; but it vanished as soon as it brought them under the trees.”
— The Lord of the Rings, Book I, Chapter 6