There is plenty of street parking that is either pay by the hour, or free depending on the block. There is also a garage on the same block (same side of the street) that is directly across from the Charles Theatre. I believe the lot right next to Metro is a pay lot, as well.
There's an open air parking lot across the street (diagonally) typically for the train station. But it's open at all hours with well-lit pay stations located in its center.
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