The Columbia Center which was formerly known as the Bank of America Tower is Seattle's tallest skyscraper at 76 stories and more than 800 feet in height. It is famous among skyscraper and urbanity fans for its unique and elegant design. You can even find it in the current version of the computer game Sim City.
You can see it from almost everywhere in the downtown area and even farther so you don't really need directions to get there. It's the tall black tower made of glass.
A parking lot resides directly across a street from the tower.
There's a Starbucks on the ground floor and the four following floors have little restaurants like a food court and places to eat. You can navigate these floors with escalators. The main elevators are more farther up.
There is also an observation deck on the 73 floor. You can get to it by asking at the info desk or try to find the right elevator. You have to use more than one really and you could get lost trying to find the second one so maybe you should ask for directions. Once you're up there, pay your admission and enjoy the view. It's not 360 degrees but you can still see downtown, the Space Needle, the waterfront, interstate 5, Pike Place Market (look for the narrow green roof), and the Harborview Medical Center.