Hidden Valley Observatory (HVO) is located at 4715 Hidden Valley Road, Rapid City, South Dakota, which is near St. Martin’s Monastery and Terra Sancta Retreat Center. The markers below show the location of the gravel road that leads to the observatory, as well as the location of the observatory, itself. It’s only ~100 yards on gravel to the observatory. The nights of public workshops a sign will be present at the gravel road entrance.