Where is the entrance to Seattle King Street Station?

You know, I have used this train station quite a few times in my life but I still do not know where the heck is the actual entrace to the !@#$ thing -- I mean, you can take a long walk to King Street and go around but given the amount of buses, light rail, and even a streetcar on the corner on S Jackson between 4th Av and 5th Av, surely there's a proper entrance tucked away somewhere...? Here's the little plaza:

I discovered there's an elevator inside this building which does take you into the station but it certainly doesn't look like that's intended for the general public. I never have the time to explore this corner properly ... would anyone local where they have hidden the entrance -- if there's one.

Union Station is easier to access and find which I find... pretty characteristic of public transit in USA. (It hasn't been an actual station for like sixty years, obviously it is easier to find than the actual thing!)