out of the blue

"You know what I would really like to do?" she looked at me over her coffee.
"I would like to dive in the Great Blue Hole. Have you heard of it?"
I admitted that I didn't know what she was talking about.
"You should Google it. It's near Belize. I met someone who really wants to go,
too. Through a mutual friend that you don't know. She's an experienced diver."
Not being a swimmer, I smiled and nodded.
"It's one of those bucket list items. You can swim through caves with a guide.
You can look up and see hammerheads."