You can park first in the garage and follow the elevators to hotel lobby. You can also sneak out around front if you find parking on street level. Upon check in they will give you a parking ticket you can scan for in and out access as you please for the duration of your stay.
I got a great parking spot--closest one to the hotel entrance. They validated my ticket when I checked in. Really makes no difference. BTW, my room had no fridge or microwave and there was nothing special about the room. I'd been at Embassy Suites, a block away, and the suite was magnificent. No comparison in it and the Hilton. Hilton has the beautiful, grand lobby, but Embassy had the great suite, including living room and kitchen.
If you check in first they assign you a spot and validate parking... makes it easier but either way works
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