Lot of bus departure gates there. Just go to the info counter, straight in from the main entrance doors.
If you are not there yet, you still have time to change your mind. Just say no. I used to hate walking until I rode 12 different Greyhound buses on my trip across America and then I realized walking 25 miles a day was a whole lot less painful than riding the bus.
If you go in at street level, it is 2 escalators down. At one of the gates numbered 81-85
It varies you have to ask when you get there.
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