This is located underneath the Kyoto Station Building, however we went out the station building and down another entrance to get into Porta. This place is just huge, with all of the city transport coming together in one place. It's madness. Once you get down to porta though, it is easier to find your way around and grab some food.
We ate at a place called Japanese Bowl Cafe and it was fantastic! Great food, reasonable price, and we got to sit and rest our feet for awhile.
I think it's open daily until about 8:30 pm, but we went for lunch.