A family’s fun day at the beach nearly turned into a nightmare when their children unknowingly played on a World War II bomb buried in the sand.

While visiting a beach in Burry Port, Wales, Kelly Gravell and her two kids, Erin and Ellis, spent time jumping on what they believed was a seaweed-covered buoy. But just days later, park rangers discovered the object was actually a 70-year-old unexploded mine from WWII.

A bomb squad was called in and safely carried out a controlled detonation, with dramatic footage capturing the powerful blast. The children’s father, Gareth, reacted on social media, tweeting, “So the buoy my kids were jumping on all weekend turns out to be a WWII bomb. Oops.”

“We were so close to disaster—it’s really shocking,” Kelly later said. Although shaken, the family says they’ll return to the beach, but with a lot more caution next time.

Local authorities have since reassured the public that the area is safe and reminded beachgoers to report anything unusual. It’s a sobering reminder that remnants of history can still be hiding in plain sight.