Congress Hall now awaited us, but I will omit a description of it, as Musical Hall, which immediately succeeded, contains so much more that is interesting. On entering, our attention was first directed to an aperture wide enough for the admission of a man's head. Any sound made in this opening is taken up and repeated by echo after echo, till the very spirit of music seems awakened. Wave after wave of melodious sound charms the ear, even if the first awakening note has been most discordant. If the soul is filled with silent awe while listening to the unseen waterfall in Cataract Hall, it is here wooed into peace by a harmony more perfect than any produced by mortal invention. A temple-cavern vaster than Ellora with a giant 'lithophone' for organ! The second wonder of Musical Hall is a lake of great extent, and from ten to thirty feet in depth. The smooth surface of these crystal waters, never ruffled by any air of heaven, and undisturbed save by the dip of our oars as we were ferried across, the utter darkness that hid the opposite shore from our straining sight, the huge rocks above, whose clustering stalactites, lighted by our glimmering lamps, sparkled like a starry sky, the sound of the far-off waterfall, softened by distance into a sad and solemn music, all united to recall with a vivid power, never before felt, the passage of the 'pious AEneas' over the Styx, which I had so often read with delight in my boyhood. I half fancied our Yankee Bob fading into a vision of the classic Charon, and that the ghosts of unhappy spirits were peering at us from the darkness. At the end of the lake is Annexation Rock, a huge limestone formation in the shape of an egg. It stands on one end, is twenty-eight feet in diameter, and over forty in height. We were now introduced into Fat Man's Misery, where the small and attenuated have greatly the advantage. We emerged from this narrow and difficult passage into the Museum, half a mile long, and so called from the number and variety of its formations. We did not linger to examine its curiosities, but pushed on over the Alps, which we surmounted, aided partly by ladders. Very steep and rugged were these Alps, and quite worthy of the name they bear. We descended from them into the Bath-room, where a pool of water and sundry other arrangements suggest to a lively imagination its designation. It certainly has the recommendation of being the most retired bath-room ever known. That of the Neapolitan sibyl is public in comparison to it. We then entered Pirate's Retreat. Why so named, I can not guess, for I doubt if the boldest pirate who ever sailed the 'South Seas o'er' would dare venture alone so far underground as we now found ourselves.