In Czechia beavers built a dam in 2 days, which local authorities had been planning for 7 years

[Nittersing]

5. I remember reading about the unexpected changes due to wolves being re-intro'd to Yellowstone

It's just astounding!

Here's a good overview for any who may not be familiar: https://www.yellowstonepark.com/things-to-do/wildlife/wolf-reintroduction-changes-ecosystem/