It’s just a room upstairs, in an old two-story house. They say when it opened, on December 1, 1868, 150 watched the Tanner Troupe perform a song and dance revue at the “Brick Building.”

A reviewer fainted with damning praise: “Notwithstanding the perfectly apparent indisposition of Mr. Tanner,” — he died two weeks later — “the bronchial affliction of Miss Soledad, the rawness of the novices, the defective musical arrangements, the want of capacity in the seating room, we may be pardoned for saying that our theater is a success.”

Legend has it that to save room, women were asked not to wear hoop skirts or petticoats. Even so, at least half the audience must have watched through open windows on the balcony. Either that or the theater extended farther back than it does today.

The “Brick Building” is the Whaley House, 2476 San Diego Avenue, Old Town. Built by Thomas Whaley in 1857, on land formerly used for public hangings, it’s renowned for a spook on the 14th stair and a cat’s ghost streaking from the outhouse across the lawn and through the dining room wall.

It also has a general store and a courtroom, plus a treasure trove of period furniture, utensils, fabrics, textures and sculpted molding, and 19th-century lighting.

The little theater’s on the southwest corner, second floor. With just a few rows of wooden captain’s chairs, a small raked stage, and a painted backdrop, it’s more intimate than the Old Globe’s White Theatre, Ion’s BLKBX space, and the Arthur Wagner Theatre at UCSD’s Galbraith Hall.

It’s not the original, which didn’t last long (in August 1869, the County of San Diego rented it as a storage space). But it’s a gem in itself.

Save Our Heritage Organisation (SOHO) restored the theater beginning in 2001. It seats, at most, maybe 25 people — comfortably, that is.

But not for a theatrical production.

“The house is a museum, not a theater,” says Welton Jones, the longtime theater critic who was among those who urged its restoration. “It’s fragile, and there’s no way to do proper lighting.”

So in a sense my favorite San Diego theater is the most intimate, and minimal, of all. Just a small, empty stage, an organ stage right, thick curtains pulled to the sides, house seats — but no performers. So you can create the story, costume the actors, block their movements, cue their songs, and live the entire experience in the privacy of your imagination.