If you would not mind a walk, you can find street parking in one of the housing areas around 10 min (walking) from Rockville Town Center! Parking is validated and first 2 hours should be free in the garages though.
Best to have the MobileNow app installed and setup before going; makes parking very easy.
There are two parking garages as well as street parking. All are metered.
Park in the town center lot. Spice xing offers two hour validation.
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