re: Turtle Tunnels

This appears to me to be an ideal situation for gifting a project, plus you get to keep the removed interior. It looks like removal of the core via chainsaw didn't yield very big or long pieces of the maple, but perhaps big enough for making pens.
I gave savaging the interior as one nice chunk some thought. Maybe you can separate the shell and core by standing on end, slowly driving a hefty chisel down around the circumference, thus popping it out. Hopefully, with nice straight grain, it would work as I'm imagining it. If not, you haven't lost anything.
I'm sure you've made the turtles' day.