The notes on one of the drawings says the tunnels go to James Caan, Jack Nicholson, Kirk Douglas, and Warren Beatty. The house on the left in the lower drawing was Warren Beatty's.

This article on the Playboy site tells about the tunnels and even has some construction photos: https://www.playboy.com/read/tunnels-to-celebrity-homes-playboy-mansion

Note the date of the article, April 1, 2015 and the following note at the end of the article:

"This is all the info we’ve been able to dig up. So we’re asking for help. If you were at the Playboy Mansion in the 1970s or 1980s, and you (or your dad or someone you know) saw or used one of these celebrity tunnels, please let us know. (But first, check the date of this article. Happy April Fools’, friends!)"