Willow Falls Trail 
We visited Willow River State Park in the winter, but it is accessible year-around and I want to take my kids back camping here some time.  There is supposed to be good fishing in the area that my son would love.  We wanted to see the falls in the winter, so we hiked Willow Falls Trail to Burkhardt Trail, which is a moderate 2 mile hike.  There is a longer set of stairs to reach the overlook part of the trail on this hike.  We learned that there is a second parking lot past the main entrance of the park, which would be best for accessing this trail and seeing the falls.  If you hike from the main park, you will make it, it is just a longer hike.  The park does require an entrance fee of $8 (out-of-state $11) per vehicle for a day-use pass or an annual pass for $28 (out-of-state $38). We were wowed by the falls in the winter, but I am sure in the spring and summer they are just as captivating. 
Address: 
1034 Cty Hwy A
Hudson, WI 54016

Red Trail and Quarry Loop
We visited Rib Mountain State Park in peak October, and there were people everywhere!  There was a fall festival for people to enjoy the beautiful colors in Northern Wisconsin.  This park has so much to see and do.  Visit in the winter to ski, snowshoe, and the rest of the year enjoy some fabulous hiking.  The Red Trail and Quarry Loop is about 2 miles with some moderate sections in it.  The views and landscapes are breathtaking though!  You are up high enough that you look over Wausau below the park.  I would make sure you bring good hiking shoes for this hike.  The park does require an entrance fee of $8 (out-of-state $11) per vehicle for a day-use pass or an annual pass for $28 (out-of-state $38).  
Address: 
149801 State Park Road
​Wausau, WI 54401

Devil's Punch Bowl Trail is a 0.7 mile out-and-back hike.  It is an easy hike, but does require a steep set of stairs down to the bottom of the cavern.  We visited it in the winter, and it was cool to see the ice formations up close, but you can access the trail year-round.  We learned quickly to step carefully, because there were pockets of water under the snow and your feet would get very wet if you fell through the snow.  
Address: 
410th Street
Menomonie, WI 54751