I took the metro to the aquarium stop and had the Boston city go pass that got me entry
The closest parking garage to the aquarium is $40 for the day. It was a gift for me to go, so I don't know the cost. Check on the internet.
I suggest parking at a subway station and taking the T in. There is an aquarium stop on the blue line.
There's no parking there. You'll have to use a parking garage nearby
Parking in garage next door is expensive, maybe upwards of $50 p day, admission is on website, join them and get discounts
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