We like visiting Fort Wilderness. From POP you could take a bus to MK then hop on a boat to FW. You can walk through the barns and there is a nice (and relatively economical) buffet at Trail's End for dinner. You can walk through the woods between FW and Wilderness Lodge where you could see deer and other animals. You can rent bicycles to ride around here as well.
You can also take a boat between FW, WL, and CR which gives you a nice view of Bay Lake. You can get off and check out any of these resorts, and if you're at CR you can hop on the monorail to visit the Poly and Grand Floridian as well.
To get back to POP you can catch a bus in front of MK or if you wanted to go for a couple monorail rides you could switch monorails at the TTC and ride to Epcot where you could get a POP bus from there. You can also take a bus from any resort to any park or DTD and get on a POP bus there. There is a lot of exploring you can do without a park ticket. Sounds like fun, enjoy!