The lobby consists of three floors of retail/dining that acts as a cafeteria for the occupants of the the building. The double heighted waterfall sculpture at the center of the building is interesting, but all in all, this area doesn't make Columbia Center a real destination.
If you're looking for views for free, the fortieth floor is home to a Starbucks Coffee. The views are not as amazing as on the observation deck, but it is a cool place to sit and drink some coffee.
The observation deck on the 73rd floor is open on weekdays only. I personally feel this is the best viewing space Seattle has to offer. It isn't expensive, is rarely crowded, and gives you an incredible birds eye view of Seattle. One thing to note is that it is not a 360 degree view. You can't see the northern Capital Hill / U-District area. There is also an active radio station in the observation deck area that does the traffic and news updates for Seattle.
