observatory

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A building, place, or institution designed and equipped for making observations of astronomical, meteorological, or other natural phenomena.
• noun A structure overlooking an extensive view.

from The Century Dictionary.

• noun A place or building set apart for, and fitted with instruments for making, observations of natural phenomena: as, an astronomical or a meteorological observatory.
• noun A place of observation at such an altitude as to afford an extensive view, such as a lookout-station, a signaling-station, or a belvedere.

from the GNU version of the Collaborative International Dictionary of English.

• noun A place or building for making observations on the heavenly bodies.
• noun A building fitted with instruments for making systematic observations of any particular class or series of natural phenomena.
• noun A place, as an elevated chamber, from which a view may be observed or commanded.
• noun (Mil.) A lookout on a flank of a battery whence an officer can note the range and effect of the fire; usually referred to as an observation post.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A place where stars, planets and other celestial bodies are observed, usually through a telescope.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a building designed and equipped to observe astronomical phenomena
• noun a structure commanding a wide view of its surroundings