Two boys aged 13 and 14 had a lucky escape after getting trapped in a cave near Castlerock, County Londonderry.
The teenagers had been playing along the coastline at Downhill beach when they got cut off by the rising tide.
The alarm was raised when they didn't arrive home on time, sparking a massive air and sea rescue operation.
Lifeboats struggled to reach the boys as the sea was so rough, so the crew waded through the waves to save them before airlifting them to hospital.
The cave fills with water when the tide comes in
One of the boys was suffering from mild hypothermia while the other was treated for shock.
Coastguard spokesman Mark Newell said the pair had had a lucky escape as the cave floods when the tide comes in.
"If the lady hadn't reported it at that stage, we could have been dealing with something far worse," he said.