Willow is 17 months old, newly but reasonably confidently walking, she's left to potter around the bottom layer of our house while I get on with washing up, hanging the washing out, popping upstairs to fetch things etc etc, I have a stair gate at the bottom of the stairs so she can't climb up them, otherwise nothing is "baby proofed" but there's also nothing dangerous like exposed wires, chokeable items or breakables in reach.
She will generally join me to help clean or play empty the kitchen cupboards while I'm in the kitchen, she almost always follows, but if she doesn't she'll read some books to herself, run around aimlessly, empty drawers etc, I keep an ear out to make sure she's ok, and check in on her every 5 mins or so...or if it's gone particularly quiet.......