A building or dome for astronomical observations.
A tower built for the view.
After breakfast he didn't go out to the observatory, not even into the library. – Mary Marie by Eleanor H. Porter
Pardon them, and put it in your pocket, Godfrey, and come, let us go to the observatory, for the night is fine, and by now the stove will be warm. – Love Eternal by H. Rider Haggard