A house with a widow's walk, sometimes called a captain's walk.
widow's walk definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a platform with a rail around it, built onto the roof of some New England houses, as along the coast, formerly for observing ships at sea
widow's walk definition by American Heritage Dictionary
A railed, rooftop platform typically on a coastal house, originally designed to observe vessels at sea.