Between Summer Fridays and spontaneous “sick days” when the weather is particularly nice, it’s time to enjoy the city’s cultural riches. And even though this is NYC, it doesn’t have to cost anything at all if you plan ahead.

Even the most prestigious museums have days when their admission is free. Here’s our guide to hacking this city so you can have an amazing, nearly cost-free summer with our guide to the best free activities.

The Museum of the Moving Image (36-01 35 Ave., Astoria) is on a roll this year, hosting major exhibitions like "Matt Weiner's Mad Men" (which was recently extended through the end of summer), and on Fridays you can get in for free from 4-8 p.m.

From 5:45 to 7:45 p.m. on Saturdays, admission to the famed Guggenheim Museum (1071 Fifth Ave.) is pay-what-you-wish, and this summer is a great time to take advantage. Their current exhibition, “Storylines,” features works by younger artists, mostly created after 2005, and explores new ways of creating an artistic narrative of race, gender, sexuality and politics.

The admission policy at the Metropolitan Museum of Art (1000 Fifth Ave.) is always “suggested donation,” so to avoid feeling like a guilty moocher, throw them a buck (or two). But if you’re really skint, they’ll still spot you a pass to more exhibits and events than you could possibly see in a single day. The facade of the museum has just been restored with seating added along the street, so you can discuss all the cool stuff you just saw over a spread from the nearby food carts.

A branch of the Met, The Cloisters (99 Margaret Corbin Drive, Washington Heights), is a piece of living history: The architecture and gardens are modeled in the medieval European style, creating a true oasis in the city. The recommended admission price is $25, but like the Met, they'll let you in for free, too.

Do you ever look at the world around you and think, hmm, why do flies and birds both have wings? Well, if you go to the American Museum of Natural History (Central Park West and 79th St.) you can learn about convergent evolution. The suggested admission price is $22, but if you can’t swing it, they’ll still give you a tour of the universe and our own little corner of it.

What’s summer about if not communing with your inner child at The Bronx Zoo (2300 Southern Blvd.)? The entry fee is pay-what-you-wish on Wednesdays, but certain exhibits, such as the Butterfly Garden and the Congo Gorilla Forest, are not included. 

On Fridays after 4 p.m., admission to the New York Aquarium (602 Surf Ave., Brooklyn) is p ay-what-you-wish. So if sharks, rays and turtles are your favorite creatures and you’re saving your pennies for other weekend activities, this is a great option for a mellow Friday night.

Admission to the Bronx Museum of the Arts (1040 Grand Concourse) is totally free, so make the trek to check out some truly boundary-pushing artwork here, from exhibits like “Secrets, Boundaries and Video Games,” about the invisible lines that separate our inner and outer selves, and “Please Touch,” Raul Mourao’s exploration of NYC’s “characters, architecture, objects and accidents.”

The National Museum of the American Indian (1 Bowling Green, Manhattan) contains one of the world’s most expansive collections of Native American artifacts. But beyond the objects and photographs, the museum is also a living history exhibit, with educational activities and performing art programs. And admission is totally free.

Entry to the 9/11 Memorial and Museum (200 Liberty St.) is completely free for visitors on Tuesdays after 5 p.m., but get there earlier: A limited number of tickets are available and are doled out on a first-come, first-served basis at the museum starting at 4 p.m. You can also reserve in advance online the Monday before your visit starting at 9 a.m. 

Yes, everybody turns out for the cherry blossoms at the Brooklyn Botanic Garden (990 Washington Ave.), but their sprawling grounds are a year-round oasis, with hundreds of plant varieties. It’s free all day on Tuesdays, and on Saturdays from 10 a.m. to noon.

From 4 to 8 p.m. on Fridays, admission to the Museum of Modern Art (11 W. 53rd St.) is free, thanks to a sponsorship deal with Uniqlo. Your ticket includes access to all of MoMa’s galleries, exhibitions and films. This is your must-see summer cultural destination, with special exhibitions of Yoko Ono, Andy Warhol, Martin Scorsese movie posters and more.