Wow is all I have to say!
Any direction you go has amazing trails. Starting with the popular Mount Helena trail system that starts right out of downtown. With over 506 mountain biking trails this system offers whatever you are looking for.
If you are looking to get an early ride in before work and only have an hour, great! Smash a quick lap on Rent Money or Entertainment.
If you are looking for something more than that, this system has so many options you can link numerous trails together for a big epic ride. It has something for everyone. From beginner to advanced riders.
There are also more remote options as well like Muskrat creek in the Elkhorns that you can turn into a 20 mile loop. Then swing in the town of Boulder for a beer and one of the best steaks you will ever eat at the Winsor bar!