But only if you’re an Illinois resident.

Tomorrow is Illinois Resident Discount Day at the Shedd Aquarium and the Adler Planetarium. General admission is free to anyone who lives in the state, though you do still have to pay for special shows and exhibits. This deal extends through Wednesday for the Adler, but then you can’t get a gratis tour of both oceanic and outer space depths on the same day.

And hey, how can you say no to scientific exploration on the cheap?