When your adult child comes home from uni and takes over your kitchen with their friends while you read a book in the next room. Big bonus if they offer you cups of tea and whatever they're cooking from your leftovers and then clean up after themselves.
It's just a perfect feeling, like everything is right with the world, and I didn't know about it until recently.
Just seemed like something worth sharing, there isn't enough said about this stage of parenting in my opinion. It can be hard, very very hard, but it can still be lovely.