TTT - The Orthanc

A great ring-wall of stone, like towering cliffs, stood out from the shelter of the mountain-side, from which it ran and then returned again....One who passed in and came at length out of the echoing tunnel, beheld a plain, a great circle, somewhat hollowed like a vast shallow bowl: a mile it measured from rim to rim. Once it had been green and filled with avenues, and groves of fruitful trees, watered by streams that flowed from the mountains to a lake. But no green thing grew there in the latter days of Saruman. The roads were paved with stone-flags dark and hard; and beside their borders instead of trees there marched long lines of pillars, some of marble, some of copper and of iron, joined by heavy chains....
To the centre all the roads ran between their chains. There stood a tower of marvelous shape. It was fashioned by the builders of old, who smoothed the Ring of Isengard, and yet it seemed a thing not made by the craft of Men, but riven from the bones of the earth in the ancient torment of the hills. A peak and isle of rock it was, black and gleaming hard: four mighty piers of many-sided stone were welded into one, but near the summit they opened into gaping horns, their pinnacles sharp as the points of spears, keen-edged as knives. Between them was a narrow space, and there upon a floor of polished stone, written with strange signs, a man might stand five hundred feet above the plain."

--TTT, "The Road to Isengard"