Gandalf relies on Legolas's sight to see Edoras in the distance

A bitter chill came into the air. Slowly in the East the dark faded to a cold grey. Red shafts of light leapt above the black walls of the Emyn Muil far away upon their left. Dawn came clear and bright; a wind swept across their path, rushing through the bent grasses. Suddenly Shadowfax stood still and neighed. Gandalf pointed ahead.

‘Look!’ he cried, and they lifted their tired eyes. Before them stood the mountains of the South: white-tipped and streaked with black. The grass-lands rolled against the hills that clustered at their feet, and flowed up into many valleys still dim and dark, untouched by the light of dawn, winding their way into the heart of the great mountains. Immediately before the travellers the widest of these glens opened like a long gulf among the hills. Far inward they glimpsed a tumbled mountain-mass with one tall peak; at the mouth of the vale there stood like a sentinel a lonely height. About its feet there flowed, as a thread of silver, the stream that issued from the dale; upon its brow they caught, still far away, a glint in the rising sun, a glimmer of gold.

‘Speak, Legolas!’ said Gandalf. ‘Tell us what you see there before us!’

Legolas gazed ahead, shading his eyes from the level shafts of the new-risen sun. ‘I see a white stream that comes down from the snows,’ he said. ‘Where it issues from the shadow of the vale a green hill rises upon the east. A dike and mighty wall and thorny fence encircle it. Within there rise the roofs of houses; and in the midst, set upon a green terrace, there stands aloft a great hall of Men. And it seems to my eyes that it is thatched with gold. The light of it shines far over the land. Golden, too, are the posts of its doors. There men in bright mail stand; but all else within the courts are yet asleep.’

‘Edoras those courts are called,’ said Gandalf, ‘and Meduseld is that golden hall. There dwells Théoden son of Thengel, King of the Mark of Rohan. We are come with the rising of the day. Now the road lies plain to see before us. But we must ride more warily; for war is abroad, and the Rohirrim, the Horse-lords, do not sleep, even if it seem so from afar. Draw no weapon, speak no haughty word, I counsel you all, until we are come before Théoden’s seat.’

The Two Towers, Book Three, Chapter 6: The King of the Golden Hall.