Wikipedia: "Titicaca is notable for a population of people who live on the Uros, a group of 42 or so artificial islands made of floating reeds (totora, a reed that abounds in the shallows of the lake). These islands have become a major tourist attraction for Peru, drawing excursions from the lakeside city of Puno. Their original purpose was defensive, and they could be moved if a threat arose. Many of the islands contain watchtowers largely constructed of reeds."