At Thoul's Paradise, perdustin posted a copy of a beautiful map of Iceland c. 1590, which includes a bestiary of sea monsters believed to infest the waters of the North Atlantic.
Two things jump out at me. First, the map includes features such as ice and trees, the latter described as windthrow from Norway. I like encounter tables which include features like this, both for local color which brings life to the setting and to provide the players with a potential resource to tap for their own schemes.
Second, it's a reminder of how superstitious the late Renaissance and Early Modern world remains. This map is dated just 36 years before the present year of my campaign. We haven't yet reached the cusp of the Enlightenment, and monsters and witchcraft are still accepted as real by many in the game-world. Stories of mythical beasts, rumors of dark arts - these, too, bring the setting to life, particularly when myths and mysteries have a basis in fact which can appear as well, as with the giant squid in Michael Crichton's Pirate Latitudes.