Mass dump the tile the cage is on, then undump the cage itself is what I've always done. EDIT: and claim them. I haven't played for a while, I'm getting forgetful.

And yes, people can be very creative. Farming various rare creatures (possibly via draining oceans), creating orbital magma cannons that can target any part of the world, conquering hell, creating mechanical calculators that operate on magma where an "overflow" error results in a literal overflow of magma...

You don't see that in many games. But there aren't many Turing complete games out there, either. I think Minecraft & Starbound are the only big ones, though I'm not sure if Terraria is or isn't.