The Collaborative International Dictionary
Observation deck \Ob`ser*va"tion deck\ A room or platform at a high point in a tall building with a broad view of the surrounding area. It is often an outdoor platform, but is sometimes indoors in a room with large windows to accommodate viewing.
Wiktionary
n. 1 An area of a tall building, often open to the sky, from which the public may look at the surrounding panorama 2 A building (such as a hide) from which people may observe wildlife
Wikipedia
__FORCETOC__ An observation deck, observation platform or viewing platform is an elevated sightseeing platform usually situated upon a tall architectural structure such as a skyscraper or observation tower. Observation decks are sometimes enclosed from weather, as many skyscraper decks, and may include coin operated telescopes for viewing distant features.
Usage examples of "observation deck".
On the far side of the observation deck he could see Isobel Bonterre, her wetsuit shining damply in the sun.
Beyond that there was a rear observation deck, the floor of which had for the moment been removed to reveal the cavernous baggage department.
With ringing and clanging all around him, C'tair recalled a better, more ordered time, when he'd stood with D'murr and Kailea on the observation deck above.
Ruthe paced back and forth in front of the windows of the observation deck while the assembled group settled into place.
But even these sense memories faded when he opened his eyes and looked out through the curving viewports of the Boreth's observation deck to see the Defiant being pulled through the stars at warp speed, ensnared in the purple web of a tractor beam and trailing half a kilometer behind the angular engineering hull of the advanced-technology Klingon battlecruiser.
When he'd taken her to the observation deck, they hadn't seen any other people.
We've built each of these connecting tunnels with thick Plexiglas so that it can double as a sort of observation deck.