Which sentence best reveals the author's purpose in paragraph 1?
from CHAPTER XIV of The Innocents Abroad
by Mark Twain

At Pisa we climbed up to the top of the strangest structure the world has any knowledge of—the Leaning Tower. As everyone knows, it is in the neighborhood of one hundred and eighty feet high—and I beg to observe that one hundred and eighty feet reach to about the height of four ordinary three-story buildings piled one on top of the other, and is a very considerable altitude for a tower of uniform thickness to aspire to, even when it stands upright—yet this one leans more than thirteen feet out of the perpendicular. It is seven hundred years old, but neither history or tradition say whether it was built as it is, purposely, or whether one of its sides has settled. There is no record that it ever stood straight up. It is built of marble. It is an airy and a beautiful structure, and each of its eight stories is encircled by fluted columns, some of marble and some of granite, with Corinthian capitals that were handsome when they were new. It is a bell tower, and in its top hangs a chime of ancient bells. The winding staircase within is dark, but one always knows which side of the tower he is on because of his naturally gravitating from one side to the other of the staircase with the rise or dip of the tower. Some of the stone steps are foot-worn only on one end; others only on the other end; others only in the middle. To look down into the tower from the top is like looking down into a tilted well. A rope that hangs from the center of the top touches the wall before it reaches the bottom. Standing on the summit, one does not feel altogether comfortable when he looks down from the high side; but to crawl on your breast to the verge on the lower side and try to stretch your neck out far enough to see the base of the tower, makes your flesh creep, and convinces you for a single moment in spite of all your philosophy, that the building is falling. . . .
The Duomo, close at hand, is one of the finest cathedrals in Europe. It is eight hundred years old. Its grandeur has outlived the high commercial prosperity and the political importance that made it a necessity, or rather a possibility. Surrounded by poverty, decay and ruin, it conveys to us a more tangible impression of the former greatness of Pisa than books could give us.
The Baptistery, which is a few years older than the Leaning Tower, is a stately rotunda, of huge dimensions, and was a costly structure. In it hangs the lamp whose measured swing suggested to Galileo the pendulum. It looked an insignificant thing to have conferred upon the world of science and mechanics such a mighty extension of their dominions as it has. Pondering, in its suggestive presence, I seemed to see a crazy universe of swinging discs, the toiling children of this sedate parent. He appeared to have an intelligent expression about him of knowing that he was not a lamp at all; that he was a Pendulum; a Pendulum disguised, for prodigious and inscrutable purposes of his own deep devising. . . .
This Baptistery is endowed with the most pleasing echo of all the echoes we have read of. The guide sounded two sonorous notes, about half an octave apart; the echo answered with the most enchanting, the most melodious, the richest blending of sweet sounds that one can imagine. It was like a long-drawn chord of a church organ, infinitely softened by distance. I may be extravagant in the matter, but if this be the case, my ear is to blame—not my pen. I am describing a memory—and one that will remain long with me.