Caribou Road starts in the town of Nederland and climbs to the old ghost town of Caribou. The road is a smooth grade dirt road that steadily climbs 1700ft over its 5.5 mile length. It starts off with quite a few houses but get quieter as you ascend. Near the end, at 4.9 miles, stay right on the main public road and don't take the private mining road to the left.
A few ruins remain of the original town, most notably the foundations of the Sherman House hotel, the Assay Office, and a couple of cabins. During fall, Caribou Road is a good way to enjoy the changing Aspens.
From Caribou, there are multiple choices of where to go from there. Descending Caribou Flats makes a good loop back to town.
Convenient parking is available at the RTD park and ride. Better yet, catch the bus from the Boulder station (bikes allowed on rack and undercarriage), link up a bunch of trails, and take your pick of multiple routes back to Boulder.