From 1-40: Raleigh-Cary-Apex: NC 157 (Guess Rd.) is exit 175 off of I-85 in Durham. If I was on I 40 I would cross over at I-540 to 70W and go to I-85 S. If you are coming from Apex you might be better off to go 55 through Durham to I-85 then go S a couple exits to Guess Rd. After that the directions you have are pretty good. You can watch for the Orange Co line and the entrance is a half mi or so beyond that.
Chapel Hill, especially the Carrboro side : Take Old 86 through Calvander and turn R on New Hope Church Rd. At the stop sign at the end of New Hope Church turn R on Old NC 10. Go about 2 mi and turn L on Mt. Herman Church Rd. Go straight at the stop light at 70 and the road name changes to Pleasant Green Rd. Go about 5 mi and at the 4 way stop turn R on St Marys Rd. Go about 3 mi and at the light turn L on Guess Rd(157). Go about 2 mi, pass a Citgo station on L and after entering Orange Co go about a half mi and turn R into park.
If coming from Hillsborough take St. Marys Rd out to Guess Rd. If coming from the W on I-40/I-85: Take I-85 at the split and get off at Exit 170. Go back a short distance towards Hillsborough and at the light turn R on Pleasant Green Rd. At the 4 way stop turn R on St Marys Rd. Go about 3 mi and at the light turn L on Guess Rd(157). Go about 2 mi, pass a Citgo station on L and after entering Orange Co go about a half mi and turn R into park.