I don't believe there is any mention of Jesus during those years, so as far as I am aware, there isn't a specific extract. He could have gone anywhere. We just don't know.
Cross referencing several verses in separate Gospels indicates the people in the area were well acquainted with Yeshua indicating knowledge gained over a significant period of time... Matthew 13:54-58 as an example:
"...He went away from there and came to his hometown, and his disciples followed him... many who heard him were astonished, saying, "Where did this man get these things? ... Is not this the carpenter, the son of Mary and brother of James and Joses and Judas and Simon? And are not his sisters here with us?" ...And Jesus said to them, "A prophet is not without honor, except in his hometown and among his relatives and in his own household." ... he marveled because of their unbelief..."
Age 30 seems important taking into account the times and customs. Although deemed an adult at age 13 following bar mitzvah a Jewish man would not be considered wise nor achieve elder status until age 30... Luke 3:23 states "... when He began His ministry, Jesus Himself was about thirty years of age�
But that also hints that he'd been away a while, doesn't it, Clanad? After all, they're saying, in effect: 'Hang on, I remember you, you were a carpenter, you used to live here; where have you been, to learn all this stuff, since I saw you last?'
The Cornwall/Glastonbury speculation isn't utterly fanciful - there was quite an international trade in Cornish tin - but there's no actual evidence for it or for anything else; I don't know why.
I found Clanad's reply confusing too. The text seems to suggest that Jesus had left his home town, but it doesn't suggest he was away for a very long period, and neither does it suggest he travelled abroad - rather the opposite, since he returned with disciples in tow. It seems that on his return people of his home town recognised him easily, which would indicate that, on that one occasion at least, he hadn't been away from boyhood until he was 30.
I've always thought that his philosophy encompasses something of the Eastern religions, in particular Buddhism, and I believe there is every possibility that he travelled abroad during those years. I wonder if the elusive 'three wise men from the East' played a part in his education?