The day grew lighter and warmer as they floated along. After a while the river rounded a steep shoulder of land that came down upon their left. Under its rocky feet like an inland cliff the deepest stream had flowed lapping and bubbling. Suddenly the cliff fell away. The shores sank. The trees ended. Then Bilbo saw a sight: The lands opened wide about him, filled with the waters of the river which broke up and wandered in a hundred winding courses, or halted in marshes and pools dotted with isles on every side: but still a strong water flowed on steadily through the midst. And far away, its dark head in a torn cloud, there loomed the Mountain! Its nearest neighbours to the North-East and the tumbled land that joined it to them could not be seen. All alone it rose and looked across the marshes to the forest. The Lonely Mountain! Bilbo had come far and through many adventures to see it, and now he did not like the look of it in the least.
As he listened to the talk of the raftmen and pieced together the scraps of information they let fall, he soon realized that he was very fortunate ever to have seen it at all, even from this distance. Dreary as had been his imprisonment and unpleasant as was his position (to say nothing of the poor dwarves underneath him) still, he had been more lucky than he had guessed. The talk was all of the trade that came and went on the waterways and the growth of the traffic on the river, as the roads out of the East towards Mirkwood vanished or fell into disuse; and of the bickerings of the Lake-men and the Wood-elves about the upkeep of the Forest River and the care of the banks.
Those lands had changed much since the days when dwarves dwelt in the Mountain, days which most people now remembered only as a very shadowy tradition. They had changed even in recent years, and since the last news that Gandalf had had of them. Great floods and rains had swollen the waters that flowed east; and there had been an earthquake or two (which some were inclined to attribute to the dragon-alluding to him chiefly with a curse and an ominous nod in the direction of the Mountain). The marshes and bogs had spread wider and wider on either side. Paths had vanished, and many a rider and wanderer too, if they had tried to find the lost ways across. The elf-road through the wood which the dwarves had followed on the advice of Beorn now came to a doubtful and little used end at the eastern edge of the forest; only the river offered any longer a safe way from the skirts of Mirkwood in the North to the mountain-shadowed plains beyond, and the river was guarded by the Wood-elves' king.
So you see Bilbo had come in the end by the only road that was any good. It might have been some comfort to Mr. Baggins shivering on the barrels, if he had known that news of this had reached Gandalf far away and given him great anxiety, and that he was in fact finishing his other business (which does not come into this tale) and getting ready to come in search of Thorin's company. But Bilbo did not know it.