In April we did a similar route, in Four Mile Canyon. This time we took a left instead of a right onto the Switzerland Trail which loops back to the start via Sugarloaf Road and Boulder Canyon.
Both Four Mile Canyon and Switzerland Trail offer a quiet climbing route that quickly gets you away from the city and into the mountains.
The route is approximately 50% gravel and 50% paved roads, which makes owning and using a gravel bike worth while!
We had never been on the Boulder Canyon Bike Path before and it is absolutely lovely with smooth crushed gravel and the roaring river right alongside you.
There is some construction in Four Mile Canyon (in fact, in June of 2019, it was closed to cyclist on the weekdays!), so we had to wait for a few timed lights where it is down to one lane.
The only way back to Boulder from Sugarloaf Road is via Boulder Canyon which is highly trafficked and has a narrow shoulder (though newly paved!). You can eventually jump on the bike path, but there are a few uncomfortable miles before you get there.
Do this ride if you want a challenging long climb with mixed road surfaces and some technical challenges. You will earn the views along the Switzerland Trail, and enjoy a smooth, fun and fast downhill back to the start.
This is a pretty balanced mix of pavement and dirt: All of Sunshine is paved, between Sunshine and Four-mile Canyon is dirt. The first 4 miles of Four-mile Canyon is paved. The last 6 miles and all of the Switzerland Trail is dirt. All of Sugarloaf and Boulder Canyon is paved. The Boulder Canyon Bike path is mixed.
We enjoyed the technical terrain going left on Switzerland trail vs right. The larger rocks are more packed down and there is less of a drop off (which always freaks us out a little bit)!
At the beginning of the route, just a little ways up Sunshine Canyon, there are public bathrooms at the Mount Sanitas Trail head.
We took the Flatiron Flyer Bus in from Denver, but there is public parking all around the vicinity of the bus station/Pearl Street Mall.