https://www.google.com/search?q=ks-15676+horn+antenna&oq=ks-...
There really isn't anything magical about that building, somewhat smaller versions or larger versions are in every city in the USA and Canada. It's a CO (central office). If you see a building in a central location with a suspicious lack of windows, lots of air handlers and generators and a few local telephone company trucks parked outside, that's what it is.
Back in the day those were the central points for switching of all analog dialtone POTS phone lines. Now they are of course major fiber sites for whoever is the ILEC (incumbent local exchange carrier) in the city, which in this case is Centurylink.
Other local examples would be:
Bellingham, intersection of Chestnut street and Forest (centurylink)
Everett, 2604 Rockefeller Ave (frontier)
East Wenatchee: on Eastmont Ave, between 10th St NE and 11st St NE (frontier)
Olympia: Corner of Washington St NE and 8th ave SE, northeast side (centurylink)
Legally the building is currently a condo: CenturyLink owns a few floors, AT&T owns a few floors. The building is valued north of $9.5 million and yet nobody has ever paid any property taxes on it (except six bucks a year for the soil and weed control district).
https://cp.spokanecounty.org/SCOUT/propertyinformation/Summa...
Paying zero property taxes is a dead giveaway for undeclared federal government facilities. They're the only ones who can thumb their nose at state tax collectors and get away with it -- and they take such pride in it that they can't resist doing so, even when it attracts attention.
If you view this link in a WebGL browser you can see the spooky-looking microwave horns (since removed):
https://goo.gl/maps/b7Yjn4DkydmX8kmR9