I have been there many times and there are no big winding roads as some have described. I was there three weeks ago. Coming from Las Vegas take the Diamond RD off ramp and drive to Pahrump, Nev, then drive to Shoshone and turn right. It will take you all the way to Scotties Castle. It is a nice drive all the way. You will have some climbing before you get to Pahrump, but not too bad.
Then on the way back from the castle if you are headed to California when you get to the Shoshone little town do not turn, just keep on going and you will come out at Baker, Ca where you get back on I-15.