At an undisclosed location outside Denison, a self-sustaining house, equipped with solar panels, a diesel generator and its own water supply, is built into a hilltop and could operate off the grid indefinitely.

Though the estate is listed for sale, the owners of the property asked that the address and their names not be published in order to protect their privacy and the nature of the estate. Terrin Bertholf, the listing real estate agent with Easy Life Realty, said the home is environmentally friendly, and the technology invested into the house related to its self sustainability pays for itself.

“There’s definitely a comfortable feeling you have knowing if you get stuck in an ice storm, or the power goes out across the whole grid, your house can still provide all of those things for basic living,” Bertholf said.

The gated entrance to the 32-acre property is discrete and easily missed from the roadside. The property is surrounded by dense woods that help conceal the estate and gives it an isolated feel. From the public road, a gravel drive leads past a stocked pond, about an acre in size, to a second gate uphill. The second gate is more secure and is situated on a 10-foot tall chain-link fence that surrounds the upper eight acres around the house. Bertholf noted the links in the fence are of a thick gauge, and the posts are embedded into concrete multiple feet into the ground.

Past the gate, the gravel drive continues on to the 3,035-square-foot house and offers plenty of parking spaces near the front facade. The stone bunkerlike house, which was constructed in 1984 and built into the hill, also resembles a castle, not unlike something found on an European landscape. Though there is an entrance on the front, a walkway leads to the back of the house to a patio area. The patio with well-manicured flower beds is covered by a pergola and features a grilling station.

Going inside through the back door, the first thing of note is the size of the walls. The exterior walls are two feet thick: eight inches of granite and marble, one foot of concrete reinforced with two mats of braided steel, four inches of extruded polystyrene insulation. The windows feature multiple levels of panes and each pane is about four-inches thick.

“This whole house is a monolithic pour, so the foundation, walls and the roof are all one pour of concrete,” Bertholf said. “The roof itself is one foot of concrete with earth on top.”

The back door opens to the central, main living space with a connected formal dining area. A marble fireplace with stone mantels is situated in the corner, and the kitchen is just off the space. Throughout much of the house, the floors are covered in Tennessee slate. The house features three bedrooms, two bathrooms.

At the end of the kitchen area is a breakfast nook with built-in China cabinets. Solid metal air ducts run across the house on the ceiling and are covered in wood or mirrors. Off the kitchen is a spacious pantry and laundry room, which features plenty of storage, a built-in desk, counter tops and space for two extra refrigerators.

A hallway from the main living room leads to a bedroom suite. The bedroom, currently opened to form one room, can be divided into two. The bathroom off the hallway features a cavelike step-down shower.

On the opposite end of the main living room is the master bedroom suite. The master bathroom features double copper sinks, a built-in vanity and granite counter tops. It also has another but bigger cavelike step-down bathtub and shower with a built-in bench.

Off the master suite, a door leads to a multiple purpose room that currently features an office space and a sitting area. In the corner of this room is a hot tub built into the ground. The hot tub is enclosed in glass and has a rock feature that matches the fireplace.

Another door leads to a spacious exercise room that could serve additional purposes. The room has a small wet bar near the entry, and a storage room with extra refrigerators and space to store provisions is off this space.

Another door off the exercise room leads to the mechanical room that houses an advance air filtration system, a reverse osmosis water filtration system and the geothermal heating and cooling system. The room holds multiple water storage tanks that feed from a 700-foot well on the property, and an electric box is also in this room that contains a master switch that can turn the property off the grid.

Back to the exercise room, a third door leads to the workshop. The ceiling of the massive workshop is supported by steel I-beams and the space contains a custom-made generator. Though 80 solar panels are on the roof of the house, the backup generator can power the property for months if needed. Double oversized wooden doors with an extra interior sliding steel cover lead to the front of the house.

Steps near the back patio go above the house to the other side of the hill and lead to a separate office building that could be converted into a guest suite. The homeowner noted the 600-square-foot building, which shares a similar design and appearance as the main house, was constructed first as a proof of concept.

“It’s a smaller replica of the house, and he built it to make sure he had a model to base it on,” Bertholf said.

The homeowner noted he began forming the ideas behind this house while he was in high school, and it became kind of a passion project that eventually came to fruition. He noted the he wants the next owner to really take care of the property and appreciate the work it took to create this estate.