Uppsala, Sweden, 1539.

A priest by the name of Olos Magnus is hunched over a very unusual manuscript, toiling away by candlelight. This manuscript is a map of what is today Scandinavia. Much of it is covered

with water and in that water are monsters. There's this great monster called the sea orm that is like a 200 foot long serpent with flaming eyes that was in the map is shown like basically wrapping itself around a large ship and just

squeezing it. There are other monsters with hooked teeth and there are monsters that look like they have

acne.

Some of them you could tell are based on animals that we know,

like the narwhal, which the male narwhal has this long tusk-like tooth.

And Olus Magnus called it the unicorn fish. I mean they're just kind of charming.

I'm Amanda McGowan and this is Atlas Obscura, a celebration of the world's

strange, incredible, and wondrous places.

While our understanding of the sea has changed quite a bit since 1539,

there are still huge swaths of the ocean that remain just as mysterious today as they were to Olas Magnus.

So on today's show we're going deep and taking a trip to the twilight zone of the deep ocean. Journalist Susan Casey takes us there after the the I think a lot of the times people expect it to be dark they expect it to be big they expect it to be scary but I'm not sure that you can really expect how beautiful it is. This is journalist Susan Casey. You could say that the ocean is her life.

She's written books on Great White Sharks on Big Wave Surfers, and she's also been a competitive swimmer, free diver and scuba diver.

Her new book The Underworld is all about the relationship between humans and the mysterious deep ocean.

But her journey begins on dry land in Uppsala, Sweden to visit a very

unusual manuscript known as the Karta Marina. The Karta marina is a map that was drawn by a Catholic priest and historian in 1539.

It's a huge map.

It's 23 square feet and it takes up an entire wall at this amazing library in

up Sala called Carolina Red Viva. I kind of made a pilgrimage there to see the

Carter Marina because it represents going back almost 500 years a time

when they didn't know what was in the ocean they drew monsters and that was

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