roverandom

Tolkien's Roverandom, about a little puppy who becomes entangled with wizards and subsequently has adventures on the moon and the bottom of the ocean, contains the following passage:

Another time he {Uin, the oldest whale} took them {Roverandom and the Mer-dog} to the other side (or as near as he dared), and that was a still longer and more exciting journey, the most marvellous of all Roverandom's travels, as he realised later, when he was grown to be an older and wiser dog. It would take a whole of another story, at least, to tell you of all their adventures in Uncharted Waters and of their glimpses of lands unknown to geography, before they passed the Shadowy Seas and reached the great Bay of Fairyland (as we call it) beyond the Magic Isles; and saw far off in the last West the Mountains of Elvenhome and the light of Faery upon the waves. Roverandom thought he caught a glimpse of the city of Elves on the green hill beneath the Mountains, a glint of white far away, but Uin dived again so suddenly that he could not be sure. If he was right, he is one of the few creatures, on two legs or four, who can walk about our own lands and say they have glimpsed that other land, however far away.
"I should catch it, if this was found out!" said Uin. "No one from the Outer Lands is supposed ever to come here, and few ever do now. Mum's the word!"

Now, where do you suppose he was reffering to? ; )