As we reckon with summer’s departure, there are a variety of fun-filled events to welcome the first signs of fall. Visit two “carnivals,” each with its own twist: huzzah and hurrah with medieval jest at the Brighton Bazaar’s Knight Carnival or tinker and test interactive exhibits at the Cambridge Science Carnival. Also, Somerville celebrates its prized, local invention, Marshmallow Fluff, with the 20th annual Fluff Festival, complete with sticky games and extra sugary challenges.

Here are six no-cost activities and events for the week of Sept. 15-21, as well as two ways to save on the arts this season.

BOOK LOVERS UNITE If a book club had a silent disco equivalent, it might be the Boston Figurative Art Center’s BYOBook event. Unlike a traditional book club, everyone brings whatever book they’re currently reading to a guided discussion with fellow readers from 7-7:30 p.m. After, attendees are welcomed to read as they please on the studio’s couches or lounge area. Snacks and beverages from the studio will be available. Sept. 17, 7-9 p.m. Boston Figurative Art Center, 285 Washington St., Somerville. bostonfac.com

KNIGHT MARKET The Brighton Bazaar, in collaboration with roving merchant curators Medieval Merriment, will transform into the first-ever Knight Carnival for a night of Middle Ages-themed mischief. Immerse yourself in a live sword fight between armored knights from local melee club North Horde, a creature puppet show, fantasy-inspired musicians, a site-wide scavenger hunt, and a costume contest for attendees dressed in their Ren Faire best. If you have gold in your inventory to spend, vendors will be selling trinkets all night. Sept. 18, 5-10 p.m. Charles River Speedway, 525 Western Ave., Brighton. facebook.com/thebrightonbazaar

AUTUMN LEAVES The Boston Landing Fall Crawl celebrates the arrival of the season with a reptile show with snakes and lizards, pony rides, and pumpkin decorating. DJ Dukes will play a live set from 11 a.m.-2 p.m., and country singer Louis Bello will pick up from 2-4 p.m. Meanwhile, from noon-2 p.m., attendees can join a line dancing lesson. Churros are on the house (while supplies last), and barbecue eats and other Southern staples will be available for purchase. Sept. 20, 11 a.m.-4 p.m. Boston Landing, 92 Guest St. bostonlanding.co

MARSHMALLOW MADNESS Don’t expect to come out of this one clean: Somerville, the birthplace of Marshmallow Fluff, celebrates this sticky-sweet legacy with the 20th annual Fluff Festival. In addition to live music and entertainment, the event will host unique games for prizes, including Fluff jousting, where participants use pool noodles with Fluff to knock others off a balance beam, and a Fluff hair-styling contest, where Fluff and Teddy peanut butter are provided for contestants to style the best ’do. .Attendees who arrive by cycle can access two free bike valets — one in front of Gracie’s Ice Cream and another by the intersection of Somerville Avenue and School Street. The fest is free to attend, but marshmallow-y foods and drinks will be available for purchase. Sept. 20, 2-6 p.m. 366 Somerville Ave., Somerville. flufffestival.com

UP, UP, AND AWAY The City of Quincy celebrates its 400th birthday with a Hot Air Balloon and Laser Light Show at Merrymount Park. On Pageant Field, attendees can play lawn games or journey 60 feet in the air in tethered hot air balloons. Meanwhile, roving costumed performers and food trucks can be found on Adams Field. At 9 p.m., the laser show begins, projecting streams and beams onto the overhead balloons and trees. Sept. 20, 4-10 p.m. Merrymount Park, Quincy. Reserve free balloon ride vouchers on the event’s website. quincy400.com

SCIENTIFIC WONDERS More than 150 booths showcasing STEAM’s finest (and most fun) will occupy the 17th annual Cambridge Science Carnival. Visit a robot petting zoo — featuring robots of the underwater, basketball, and gummy bear varieties — check out hands-on booths to make stomp rockets, sugar glass, or bath bombs. Members of the MIT Physics Department will perform demonstrations at 1 and 3:15 p.m., and the hosts of the “Tumble Science” children’s podcast will perform interactive songs at 1:45 p.m. Sept. 21, noon-4 p.m. Kendall/MIT Open Space, 292 Main St., Cambridge. cambridgesciencecarnival.org

Deals and Steals

FINE FOR FIVE Starting Sept. 18, the Museum of Fine Arts kicks off its $5 Third Thursdays programming. On the third Thursday of each month, from 5-10 p.m., general admission is pay-as-you-wish with a $5 minimum. A crisp Lincoln grants access to the main galleries, as well as special after dark programming exclusive to each event — this month is Latinx Heritage Night featuring drop-in art sessions to make Puerto Rican beaded bracelets and Ex-Votos paintings, live sets by the Rafa Moreno Band and DJ Montro, and special spotlight talks and guided tours. mfa.org

SYMPHONY SEASON PASS Full-time Boston students with a valid college ID can take study breaks with an (award-winning) symphony when they purchase a $20 H+H Masterpass. The exclusive pass can be redeemed to access up to eight Handel and Haydn Society performances through the 2025-26 season. (Some exclusions apply.) handelandhaydn.org/concerts-tickets/masterpass

Check individual event websites for the most up-to-date information.

Send info on free events and special offers at least 10 days in advance to ryan.yau@globe.com.

Ryan Yau can be reached at ryan.yau@globe.com.