"The X-Files" star David Duchovny believes the truth is out there ... that his out-of-this-world Malibu estate is for sale for the earthbound price of $12.5 million.

This leisure paradise was built as an ultra-modern, easy indoor-outdoor living experience ... perfect for unobstructed views when watching the skies for unidentified flying activity -- or just sunsets, if you prefer.

The residence, in the exclusive gated neighborhood of Malibu's Point Dume ... 3 bedrooms in the main house, comprising 3,577 square feet -- not including the separate structure outside -- on an acre of lush land, with beach-key access to the nearby Pacific.

A gravel motor court with plenty of parking space -- for FBI vans, black helicopters, or just your SUV -- leads up to the the place, with a custom wooden front door, soaring ceilings inside, recessed lighting, and skylights throughout the place ... perfect for letting in natural light, and the occasional peek at any passing paranormal activity.

There are white oak floors in the bedrooms and en-suite baths, and the chef's kitchen has stone countertops, custom cabinets, and premium Miele appliances ... the smart-home system controls security cameras, the lighting, the intercom, and Sonos audio throughout.

There's a lap pool outside with a wood deck, near a sunken firepit with built-in seating ... and even more entertainment options, including an outdoor kitchen with a Wolf grill, mini fridge, and a dedicated dining space. Spa amenities include a built-in Jacuzzi, an outdoor shower, and a cold plunge.

The exterior building out back -- literally a transported train caboose -- can be set up as a gym, office, or a guest suite. It has pocketing glass doors, a covered deck with built-in heaters, and an en-suite bath with a skylit-tiled shower and stone vanity.

The landscaping is lush, with mature citrus trees, and a comprehensive security system ... ensuring the property's privacy for any secret meetings, or maybe just a pool party.

Duchovny's owned the place for more than 20 years, even writing a novel and recording podcasts there. Take a closer look at this supernatural offering!