There are a couple different loops here, both about the same length.

West Loop (submitted by Rob Elliot):

This is route going up the summit of Lassen Peak combines a ride and run. The goal is to go from the very bottom of the mountain to the summit in one single, fast effort. The ride is notable and summit trail known for being one of the most popular day trips. It gets weather extremes and the peak is 10,300 ft. Hwy 89 is a popular road to ride to the summit trail, it's a mellow 16.5 miles climb that climbs about about 3000 ft and end at the trail head. It starts at the Lost Creek Campground where the road  starts to go up to Mt Lassen.

The route begins and finishes at Glenbrook in the Blue Mountains, Australia. Glenbrook is regarded as the start of the Blue Mountains National Park. It's pretty much exactly 100kms and contains around 2,500m of climbing and the same descent. 90% of the route is on fire trail and extremely runnable. There's approximately 10km of bitumen / road.