When I was young (also stupid) we were on holiday at Punta Verudela, Pula, (44.8348180, 13.8373873) and one day, that island in the distance (44.8312627, 13.8398307) looked too cool to not swim too it, and me, my dad and my brother decided to try and make it there. It looked pretty close, but I never swam so long in my life. Because we took our sweet time and had a pretty chill tempo, after about an hour, we made it! on our side it was all sheer and sharp cliffs though, so although the island was still cool and enticing, we had no idea if it was even possible to get up there somewhere, or how long it would take to swim around. Playing it safe, we swam back in about the same tempo and took another hour of relaxed swimming. Probably helped that the Mediterranean sea isn't as tidally active. Checking it now, the swimming distance seems around 440m (we approximated 1Km back then :) ) I wasn't scared at any point and just having fun, but thinking back now, so many things could have gone wrong. I think I would be a lot more afraid to try that again, without knowing what I'm getting myself into.