Just off the coast of Cornwall in the UK, two divers ran into a giant barrel jellyfish that was as big as they were.

Underwater cinematographer Dan Abbott captured the jellyfish on camera, swimming beside wildlife biologist and presenter Lizzie Daly.

The jellyfish just “appeared out of the murky water,” Daly said, bigger than any other barrel jellyfish they’d ever seen. They swam with it for about an hour, Daly told Motherboard.

“It really humbles you to be alongside an animal that size,” Daly said. “It’s an experience we’ll never forget.”

The barrel jellyfish is the largest jellyfish that lives off the coast of the UK. Also called the dustbin-lid jellyfish, they have 8 frilly arms with stinging tentacles. It’s rare for humans to swim with them, and most people only encounter them when they wash ashore.

Abbott and Daly encountered the jellyfish on the last day of Wild Ocean Week, which Daly started to inspire others and raise money for the Marine Conservation Society in the UK. Daly said the goal of the week was to show people the wildlife living nearby. The giant jellyfish was a highlight, she said, both personally and in trying to achieve those conservation goals.