Treat Avenue runs north-south through central Tucson, but it becomes a sidewalk as it crosses the Broadmoor-Broadway Village neighborhood. It's a nice place to walk; there are benches along its length. Half a block north of Arroyo Chico is a poetry mailbox: Pick up a poem, leave a poem, or write a poem while you sit on the bench: @urbanpoetrypollinators on Instagram. (If you don't have an account, I think you can click/tap on that link and scroll a bit.)
As far as I know, the mailbox doesn't have a street address. Below is a Google Map showing it:
Here's a link to that map: https://goo.gl/maps/3C3PfejUUdcwiX6H9. You can also ask your GPS for 32.217229417796304, -110.93086206093965. I was there on January 13th.