Want to help me with a painting?

The hole is where the knob would go, not the keyhole?

Could you still do a view into a room, or is that too cliched?

ETA cindy and I were typing at same time- I like hers better!!!

a butterfly or a ladybug...

You peek through a key hole to see inside a room -- so the room could be anything from realistic - a kitchen or living room -- or fanciful, a secret garden. It would probably be easier to do with the bigger hole -- but then, in looking through and seeing anything -- the bigger hole could be someplace else entirely -- a peaceful beach scene or a different room in a different house.
The eyeball idea is good too -- peeking in and out!! But eyeballs can quickly slide to creepy ...

I like the eyeball idea!

Those remind me of birdhouse openings. Since the doorknob is not there it reminds me of an abandoned house. How about a birds nest with a tiny glimpse of the interior of a room in the house.

A hallway with multiple doors.

Mine is draw a key in the final lock to show where the painting is to end.

What about a peek into a "fairy house" or "fairy garden?" Tiny furniture made from things found in nature - chairs from twigs, a woven rug from leaves, etc. You don't actually have to paint the fairies. Or you could give the illusion of their magic with some Bokeh.