If you want stuff that's close to Ft. Collins, then you could spend a day or two riding Horsetooth Mtn park/Lory State Park(they connect, and a pass to one gives access to both trail systems). They have a swim beach(horsetooth side), and camping avail. Just north of Ft Collins you could also go up the Poudre/HWY14, and hit up hewletts,youngs, and Dadds gulches. Lots of camping, and Mishawaka amphitheater is a fun place to grab a beer/bite/band. About an hour north(in WY.) there's Curt Gowdy State park, and they have a nice trail system too.