If you're looking to do something fun on Halloween that combines costumes and bikes, check out the Halloween Bike Ride, which meets up at 8pm on October 31st at the Green Street T Station (Orange line) in JP. It's free and should be lots of fun for riders of all ages.
The ride was started in 2000. The slow-paced ride covers about 18 miles as it meanders from the Green Street T Station in Jamaica Plain to Kenmore Square, Coolidge Corner, Harvard Square, Central Square, Inman Square, Copley Plaza, and back to Jamaica Plain. The route changes slightly from year to year, and may change on the night of the ride based on road conditions, and sometimes the whim of the Ride Leader. The ride is friendly, open to all, and a great way to spend Halloween Night!