A coroner said he believed a man who disappeared nine years ago "somehow died in the sea" off the East Yorkshire coast.
Russell Bohling, 18, from West Ella, near Hull, went missing on 2 March 2010.
His body has never been found but his car was later discovered at Bempton Cliffs car park, near Bridlington.
Assistant coroner David Rosenberg ruled out suicide and gave a narrative verdict at the inquest in Hull.
Mr Rosenberg said he thought Mr Bohling died on the day he went missing and "based on the submissions of the police that no body has been found, I believe somehow he died in the sea at Bempton Cliffs.
"We do not know how Russell came to die."
Mr Bohling had communication issues but was doing well as a student at Bishop Burton College on a brick-laying course, Mr Rosenberg said.
"Russell was enjoying life, enjoying independence, He had started to fly," he told the inquest.
There was not enough evidence to show whether he might have tripped and fallen or suffered an asthma attack after going in to an RAF bunker, he added.
It is known Mr Bohling had looked for information about the bunker at Bempton.
Mr Rosenberg told Mr Bohling's family "the thought of what happened to Russell will haunt you for the rest of your lives."
His father Roger Bohling, speaking after the inquest, said: "He wasn't seen, nobody saw him so there's no reason to believe he was ever on the cliff top.
"I believe he could've gone into the bunker at Bempton and had a massive asthma attack."