Well, I spent 5 of the best years of my life there......
Try out Rusty's last chance on Moro street of Aggieville. Decent bar, great fries. There is a new beer that is brewed in Manhattan, Tallgrass. Try the ale.
If there is a k-state baseball game in town, check it out.
Go to Pat's blue ribbon for the sweet potato fries.
On the west side of town there is wildcat creek on anderson, west of westloop... there is a walking trail and park there.
Tuttle creek up the road is pretty cool -- great spillway area, and you already know the offroad parts.
If old buildings are your thing, walk through the campus. Cool buildings are the Library, Seaton, Union, Allen field house.
If you need good chinese at 2 AM, look accross the street from the bars.
If you like pizza with crust to dip in honey, try Pyramid.