Although it was only for part of the day, it is an incredible milestone for the poorly youngster.
His family did not expect to be able to take him outside Bristol Royal Hospital for Children because he was still recovering from major surgery carried out the week before.
But on Thursday his parents Leah Lucas and Anthony Buckley from Illogan, were told they could take him to the local aquarium.
Leah said: "It was totally amazing we never expected it to happen after is operation and Bailey totally loved it - he loved watching all the fish and the lights.
"It was just so overwhelming and felt so real and right.
"I thought I'd be a nervous wreck, but I wasn't and everything felt so perfect."
The operation was to partly to fit a new feeding tube as Bailey cannot feed himself as well as deal with a problem of his stomach, liver and bowel being stuck together.
Doctors have started him on continuous feeds, but it is too early to tell how well he is doing.
If they can get him to feed, he will be allowed out more and, as his parents hope, will be allowed to live at home for his final months.
He was born with no pulmonary artery and other problems and was given little chance of survival, even before birth.
