Begin your cold-weather exercise transition at Prospect Park’s Wollman Rink, which will be hosting a winter-sports showcase called BeFitNYC on December 5. There will be broomball (similar to ice hockey, except with a broom and a kickball, and no skates), an obstacle course courtesy of the New York Road Runners, soccer on an inflatable field, and reps from local lacrosse, kickball, and figure-skating clubs. Bring the kids (11 a.m. to 3 p.m.; free; ice-rink admission is half-price from 10 a.m. to 1 p.m.; entrance at Parkside and Oceanside Aves.; 718-965-8999).