Any suggestions on where to let my rat explore?

Really about anywhere, My cluttered room gave them lots to explore. First trick was coming to a treat sound, so my room was like Disneyland for them,toys and hides everywhere, even a climb rope to a shelf and table.
Yes,anyplace they free run, MUST be rattie proofed any chew hazards like plastics and cords.Choke hazards, toxic things ETC.
Got a single rat and time to spend with it, try trick training, that helps them socialize, keeps them active and mentally stimulated so the don't get depressed being alone. A lot of fun for you too, you both look foreward to time together.
Out of sight inmy room,I ring a little cage bell or make a smootching sound, my ratties would come running for their treat.
A mouse I had such a strong bond with could free run the back yard and come when I called him. He loved riding in my shirt pocket when I went shopping at places like Walmart. almost no one notices him.