Thus they came at length to a wide arch with tall pillars upon either hand, hewn in the rock, and between hung a great portcullis of crossed wooden bars, marvellously carved and studded with nails of iron.
Elemmakil touched it, and it rose silently, and they passed through;..
...
"You have passed the First Gate, the Gate of Wood," said Elemmakil.

...some half-league from the Wooden Gate Tuor saw that the way was barred by a great wall built across the ravine from side to side, with stout towers of stone at either hand. In the wall was a great archway above the road, but it seemed that masons had blocked it with a single mighty stone. As they drew near its dark and polished face gleamed in the light of a white lamp that hung above the midst of the arch.
"Here stands the Second Gate, the Gate of Stone," said Elemmakil; and going up to it he thrust lightly upon it. It turned upon an unseen pivot, until its edge was towards them, and the way was open upon either side; and they passed through, into a court where stood many armed guards clad in grey.

After a little space they came to a wall yet higher and stronger than before, and in it was set the Third Gate, the Gate of Bronze: a great twofold door hung with shields and plates of bronze, wherein were wrought many figures and strange signs. Upon the wall above its lintel were three square towers, roofed and clad with copper that by some device of smith-craft were ever bright and gleamed as fire in the rays of the red lamps ranged like torches along the wall. Again silently they passed the gate, and saw in the court beyond a yet greater company of guards in mail that glowed like dull fire; and the blades of their axes were red.

Thus at last they drew near the Fourth Gate, the Gate of Writhen Iron. High and black was the wall, and lit with no lamps. Four towers of iron stood upon it, and between the two inner towers was set an image of a great eagle wrought in iron, even the likeness of King Thorondor himself, as he would alight upon a mountain from the high airs. But as Tuor stood before the gate it seemed to his wonder that he was looking through boughs and stems of imperishable trees into a pale glade of the Moon. For a light came through the traceries of the gate, which were wrought and hammered into the shapes of trees with writhing roots and woven branches laden with leaves and flowers. And as he passed through he saw how this could be; for the wall was of great thickness, and there was not one grill but three in line, so set that to one who approached in the middle of the way each formed part of the device; but the light beyond was the light of day.

...in wonder and lightening of heart he was brought to the Gate of Silver.
The wall of the Fifth Gate was built of white marble, and was low and broad, and its parapet was a trellis of silver between five great globes of marble; and there stood many archers robed in white. The gate was in shape as three parts of a circle, and wrought of silver and pearl of Nevrast in likenesses of the Moon; but above the Gate upon the midmost globe stood an image of the White Tree Telperion, wrought of silver and malachite, with flowers made of great pearls of Balar. And beyond the Gate in a wide court paved with marble, green and white, stood archers in silver mail and white-crested helms, a hundred upon either hand.
Then Elemmakil led Tuor and Voronwë through their silent ranks, and they entered upon a long white road, that ran straight towards the Sixth Gate;

...as they went the grass-sward became wider, and among the white stars of uilos there opened many small flowers like eyes of gold.
So they came to the Golden Gate, the last of the ancient gates of Turgon that were wrought before the Nirnaeth; and it was much like the Gate of Silver, save that the wall was built of yellow marble, and the globes and parapet were of red gold; and there were six globes, and in the midst upon a golden pyramid was set an image of Laurelin, the Tree of the Sun, with flowers wrought of topaz in long clusters upon chains of gold.
And the Gate itself was adorned with discs of gold, many-rayed, in likenesses of the Sun, set amid devices of garnet and topaz and yellow diamonds. In the court beyond were arrayed three hundred archers with long bows, and their mail was gilded, and tall golden plumes rose from their helmets; and their great round shields were red as flame.

...the way was short to the Seventh Gate, named the Great, the Gate of Steel that Maeglin wrought after the return from the Nirnaeth, across the wide entrance to the Orfalch Echor.
No wall stood there, but on either hand were two round towers of great height, many-windowed, tapering in seven storeys to a turret of bright steel, and between the towers there stood a mighty fence of steel that rusted not, but glittered cold and white. Seven great pillars of steel there were, tall with the height and girth of strong young trees, but ending in a bitter spike that rose to the sharpness of a needle; and between the pillars were seven cross-bars of steel, and in each space seven times seven rods of steel upright, with heads like the broad blades of spears. But in the centre, above the midmost pillar and the greatest, was raised a mighty image of the king-helm of Turgon, the Crown of the Hidden Kingdom, set about with diamonds.
No gate or door could Tuor see in this mighty hedge of steel, but as he drew near through the spaces between its bars there came, as it seemed to him, a dazzling light, and he shaded his eyes, and stood still in dread and wonder. But Elemmakil went forward, and no gate opened to his touch; but he struck upon a bar, and the fence rang like a harp of many strings, giving forth clear notes in harmony that ran from tower to tower.

(UT, Of Tuor and his Coming to Gondolin)