Ortega is great fun. Located in south orange couty, it is a tight windy road that is very dangerous at parts but so much fun to drive. You have to be careful of oncoming traffic though especially at night, since most people drive with their high beams on when it's dark it's easy to get blinded. It is quite long too. My last trip there I wend 18 miles in before I turned around. I recomend it!
Take the I-5 south and exit on Ortega, turn left and you will take a 10-ish minute drive(depending on speed and traffic) towards the canyon. The fun begins once you cross Antonio. I did it at like.. 12:30 am in my civic and it was a blast.