Jack Nicholson, Warren Beatty, Kirk Douglas and James Caan may have all been considered some of the luckiest men back in the 1970s and '80s.

Why?

These stars' homes reportedly had underground access to the Playboy Mansion in L.A. through a series of tunnels that were recently discovered when a Playboy staff member found a box containing old photos and blueprints, according to Vanity Fair.

After searching for photos for Hugh Hefner's upcoming April 9 birthday, the Playboy Mansion employee uncovered "some Polaroids from 1977 that showed a large excavation project at The Mansion."

When the staff member inquired about the tunnels, the Mansion's general manager confirmed that Hefner had the tunnels built to connect the "bunnies" to celebrities' houses.

The plans reference the homes of "Mr. J. Nicholson," "Mr. W. Beatty," "Mr. K. Douglas" and "Mr. J. Caan," which is enough information to distinguish the four highly recognizable monikers. All of the men lived near Hefner's world-renowned home during the '70s and '80s, so the underground maps could be legitimate.

The staffer said he spent nearly an hour in the unfinished basement of The Mansion and recovered what was described as a "treasure trove of old photos, plans and blueprints," Playboy reported. There were no dates on the architectural diagrams, but the Polaroids were from 1977.

The tunnels were reportedly closed in 1989, around the same time Hefner married Playmate Kimberley Conrad, and, when asked, the general manager wouldn't disclose any more information about the hidden passageways.

Hugh Hefner would not shed any light on the creation of the tunnels.

Playboy has reached out to reps for Nicholson, Caan, Douglas and Beatty, but they declined to comment.

The blueprints appear to be authentic, so we're hoping this isn't a well-thought-out April Fools' Day joke.