I know Lake Ridge. Used to work at Thackett's Mill, the comercial buildings down my the pond.
There's a triangle I ride at least once a year. You're close to part of it.
Fairfax to Occoquan on 123, Old Bridge and PW Parkway to Manassas, various roads through Manassas, Old Centerville Road and Braddock Road back to Fairfax. 40ish miles. A few hills but not bad. Not much shade, so I don't ride it this time of year.

Ever ridden up Tanyard Hill in Occaquan? It's a hoot.