AS TWILIGHT FALLS ON A SUMMER NIGHT, Michael McCulloch and Maryellen Hockensmith’s garden resonates with the vibrating wing-beats of hummingbirds. Yellow sunflowers pop against the darkening sky, and deer nibble on apples and blueberries. On this 40-acre Portland property, perched at the crest of Northwest Portland’s hills with the valley sprawled at its feet, both flora and fauna become a natural extension of the house and its inhabitants—exactly what the homeowners intended. “We wanted to extend the house into the garden and create a real outdoor living room,” McCulloch says. “Our goal is to move out here May 1 and not move back inside until late October.”

The house was designed by renowned Portland architect Pietro Belluschi. His second-to-last project, it was completed in 1980 and retains the architect’s hallmark eloquent simplicity. Hockensmith, an accomplished vocalist, bought the place in 2002 with her first husband, who passed away suddenly less than two summers later. She found solace with McCulloch, a local architect who had become close friends with her husband after designing his beach house.

When McCulloch moved in with Hockensmith in 2004, the residence was in perfect condition. Outside, however, sheep grazed in a backyard meadow of overgrown grasses and 10-foot-tall blackberry bushes. In homage to her late husband, Hockensmith contributed the lower 20 acres to the Three Rivers Conservancy, which will hold the land as a conservation easement in perpetuity. Now, she and McCulloch preserve the forested nature of the property by pulling out invasive plants, such as ragweed and thistle, so that the native Douglas fir and cedar trees can flourish.

The couple consulted with landscape designers Beth Holland, Laura Crockett, and Ann Lovejoy to create a series of basalt terraces on the remaining land. From a greenhouse full of cacti and citrus trees, the terraces tumble down the hillside along a diagonal axis, perfectly following the slope of the land and the wind’s natural path. The outdoor rooms play host both to intimate dinner parties and to spiritual gatherings, fundraisers, and events for school groups. A sliver of lawn sits at the base of the terraces, where Hockensmith’s two children, Elena and Thomas, play badminton or boccie.

Water also plays a part in the terrain. A stream and a solar-heated saltwater swimming pool, both designed by Eamonn Hughes, appear as if they had spontaneously bubbled up from the ground. Beside the pool sits a meditation pavilion built by Patrick O’Neill; it was designed by McCulloch to reflect the main house. The family slips through its sliding glass walls into the pool’s azure depths when the summer air turns velvety.

The two are content that they’ve created a landscape well aligned with nature. “We see ourselves as conservators of the place,” Hockensmith says, sweeping her arm past some spiky cattails toward the flocks of swallows swooping around the eaves of the house. “We’re trying to be stewards of the land in the most sensitive manner possible.”