This summer, the “psychogeographer” Alastair Bonnett got me thinking about what we’ve given up with our over-dependence on Google Maps: the serendipity of stumbling upon an unknown place, the disorienting thrill of getting lost. But that’s not all: What about the sea monsters?

For hundreds of years, the finest maps were decorated with exotic creatures swimming out in the nether regions of the world. If you’re missing them this Halloween season, take heart: They’re all brought back from extinction by Chet Van Duzer’s beautifully illustrated book “Sea Monsters on Medieval and Renaissance Maps,” available this month in paperback.

“Even the most extravagant medieval sea monsters on maps were drawn from sources that the cartographers believed to be reliable,” Van Duzer says. “They were included on maps as information.”

But not information as we think of information, e.g. “Siri, how do I get to the Kennedy Center?”

Van Duzer says, “Most medieval world maps, called mappaemundi, were not tools for navigation, and indeed were so vague that they would be of little use in planning a journey. Their function was didactic: They showed in a general way how the different regions of the world were situated with relation to each other. They were to be studied and contemplated, rather than used as travel guides.”

These weren’t crowdsourced documents, of course. “In the Middle Ages there was no regulation of mapmakers at all,” Van Duzer notes, “and anyone who could draw a map could add whatever outlandish creatures he or she pleased, just as a painter could add outlandish creatures to a painting.”

At a time when travel was difficult, expensive and rare, these elaborately decorated maps served as windows on the world for wealthy people — and a way off showing of their sophistication and knowledge. There’s nothing like an intimate familiarity with the hoge — it looks like an aquatic wolf — to impress your friends!

And like our UFOs and Bigfoot sightings, these monsters also tell us something about that distant age: “Sea monsters certainly expressed a fear of the unknown depths of the ocean,” he says, “and also, in some cases, of the unknown dangers of distant regions. The Indian Ocean, the most distant ocean from Europe, tends to have a higher number of sea monsters than other oceans on medieval European maps.”

Van Duzer says it wasn’t till the middle of the 16th century that cartographers gradually began to invent fantastical creatures and use them for purely decorative purposes. In the end, they were killed off by more frequent travel and more reliable science. “Nowadays, the vast majority of maps are utilitarian, so there are few sea monsters.” Sigh.

“I don’t want to suggest that artistry is not part of the creation of modern maps, but in terms of artistic objects for display and contemplation, yes, I do think that medieval and Renaissance maps are superior.”