A walking trail that dates back centuries is one of Rhode Island’s most impressive attractions. It runs alongside the Atlantic Ocean and some of Newport’s most beautiful mansions, known as ‘‘summer cottages’’ to the families that built them in the 1800s. Around two-thirds of the 3.5-mile (5.6-kilometer) trail is currently closed because of damage from Superstorm Sandy, but the most heavily traveled parts are still open. The walk runs along private property, so stopping for extended periods is not allowed. But there is a seating area along the trail outside The Breakers mansion, built for the Vanderbilts, and it’s the perfect spot to eat a picnic lunch.