Maester Luwin appears to have an observatory in Winterfell and even mentions having received a new lens for it.
"There was no rider, my lord. Only a carved wooden box, left on a table in my observatory while I napped. My servants saw no one, but it must have been brought by someone in the king's party. We have had no other visitors from the south."
"A wooden box, you say?" Catelyn said.
"Inside was a fine new lens for the observatory, from Myr by the look of it. The lenscrafters of Myr are without equal."
A Game of Thrones, Catelyn II
These lenscrafters likely make the lenses for the Far-eyes/Myrish eyes too, hence the name. These are basically telescopes and used by sailors quite a lot as well as the maesters. Maester Luwin's and Maester Aemon's Myrish eye's are also both on tripods so are likely more permanent features of the room/building.
Maester Luwin's turret was so cluttered that it seemed to Bran a wonder that he ever found anything. Tottering piles of books covered tables and chairs, rows of stoppered jars lined the shelves, candle stubs and puddles of dried wax dotted the furniture, the bronze Myrish lens tube sat on a tripod by the terrace door, star charts hung from the walls, shadow maps lay scattered among the rushes, papers, quills, and pots of inks were everywhere, and all of it was spotted with droppings from the ravens in the rafters.
A Game of Thrones, Bran VII
On the edge of the Wall an ornate brass Myrish eye stood on three spindly legs. Maester Aemon had once used it to peer at the stars, before his own eyes had failed him.
A Storm of Swords, Jon IX
On a side note astronomy in Westeros is only really important to the Maesters as they use it to tell the time/passing of the months. Many other people use far-eyes as we would use them to see further, scout ahead and keep a look out. Note that far-eyes here refers to the people using the Myrish eyes.
"Fallen," Will insisted. "There's one woman up an ironwood, half-hid in the branches. A far-eyes." He smiled thinly. "I took care she never saw me. When I got closer, I saw that she wasn't moving neither." Despite himself, he shivered.
A Game of Thrones, Prologue
High overhead, the far-eyes sang out from the rigging. Captain Moreo came scrambling across the deck, giving orders, and all around them the Storm Dancer burst into frenetic activity as King's Landing slid into view atop its three high hills.
A Game of Thrones, Catelyn IV
They were still a half day's ride from Renly's camp when they were taken. Robin Flint had ranged ahead to scout, and he came galloping back with word of a far-eyes watching from the roof of a distant windmill. By the time Catelyn's party reached the mill, the man was long gone. They pressed on, covering not quite a mile before Renly's outriders came swooping down on them, twenty men mailed and mounted, led by a grizzled greybeard of a knight with bluejays on his surcoat.
A Clash of Kings, Catelyn II