Ключевые слова: aerial, aerial imagery, aerial photography, aerial survey, ancient, architecture, bastion, blue, castle, day, defense, dungeon, europe, finland s, fortification, fortress, historical, history, island, june, kuusalmi, lake pihlajavesi, landmark, medieval, northern europe, olafsborg, olavinlinna, old, savonlinna, scandinavia, sky, strengthening, stronghold, summer, sunny, tower, travel, wall, water, water area, water surface,