ROYAL RENAISSANCE At the 23rd annual Medieval Festival, the Cloisters and nearby Fort Tryon Park are transformed into an authentic, medieval-era market village, complete with storytellers, magicians, musicians, and knights in chain armor. The program also features jugglers, jesters, and jousting matches. Revelers are invited to don period costumes worthy of the Fisher King and feast on medieval dishes. Crafts are available for purchase. The event is presented by the City of New York Parks and Recreation Department and the Washington Heights and Inwood Development Corporation. Sunday, September 30, 11:30 a.m.–6 p.m., Fort Tryon Park, between West 192nd and Dyckman streets, and between Riverside Drive and Broadway, Inwood, 212-795-1600, free.

BROOKLYN’S FINEST An introduction to the borough’s original settlers, “Native Americans of Brooklyn,” is presented by the rangers of Fort Greene Park. In a city brimming with the culture of its immigrant communities — from Chinatown to Little Italy to Flatbush and Jackson Heights — residents often overlook those who initially made their homes in this diverse metropolis. Parkgoers are given a history lesson on Brooklyn’s Algonquin inhabitants and their related indigenous groups across America. Monday, October 1, 1 p.m., Fort Greene Park. Visitors Center, Myrtle Avenue, between Cumberland Street and DeKalb Avenue, Brooklyn, 718-965-8900, free.

I COVER THE WATERFRONT Volunteers are called on to help tidy the city’s beaches and coastal areas during a citywide “Green Apple Fall Coastal Cleanup.” Saturday, October 6, 10 a.m.–2 p.m., Dyckman Marina, Dyckman Street at Hudson River, Manhattan; Pugsley Creek, between Castle Hill Avenue and Hart Street, the Bronx, and Kaiser Park, West 31st Street, north of Neptune Avenue, Brooklyn, 212-360-3317, free.

SECRET GARDEN At the New York Botanical Garden, kiku, Japanese chrysanthemums, are in bloom this fall. The “Art of the Chrysanthemums” flower show celebrates an expansive horticulture tradition that spans 1,500 years and has generated more than 10,000 styles. This rich art form has seldom been on display on such a scale outside of Japan. The program includes Japanese-themed cultural activities such as traditional song, dance, drum and samurai sword performances, tea ceremonies, origami, and flower arrangement demonstrations, as well as an exhibit of illustrated books and prints. Saturday, October 20 through Sunday, November 18, New York Botanical Garden, 200th Street at Southern Boulevard, Bronx, 718-817-8700, $5–$18. For complete information, go to nybg.org.

LIFTING AN ANCIENT CURSE… The American Museum of Natural History hosts “A Night at the Museum,” a nod to the 2006 Ben Stiller film of the same name, which was shot in and around the Manhattan institution. The museum opens its doors to overnight guests during a pre-Halloween sleepover. Although TRex won’t chase the little ones around, the AMNH promises an especially spooky slumber party. Friday, October 26, 5:45 p.m., American Museum of Natural History, Central Park West at 79th Street, 212-769-5200, $99-$109.