For years, people have gone to Signature Theatre for its award-winning plays, not its building, which was, to put it mildly, strange.

The troupe performed in a retrofitted bumper-plating factory, on a solitary strip in Arlington. Inside the dark building were a small theater, a rehearsal room and a crowded lobby, and not much else.

Tomorrow night, the new Signature Theatre opens in a glistening new building in the Village at Shirlington, less than a quarter mile from the old site. It will offer more comfort for the actors and theatergoers as well as a sophisticated technical setup that will help give plays a level of polish impossible during the company's first 17 years.

The new $16 million theater, built in partnership with Arlington County, has four times the space of the bumper place. It has two black-box theaters -- one with 275 seats that can expand to 349, the other with 99.

Despite its industrial location beside a muddy creek in Northern Virginia, Signature has won national recognition, particularly for its revivals of the musical works of Stephen Sondheim. It's also done original plays and won critical acclaim for productions of work by Cameron Mackintosh and Terrance McNally.

This milestone might be marked with a few lines from Sondheim's song "Putting It Together": "Bit by bit, putting it together / piece by piece, working on the vision night and day."

Eric Schaeffer, the artistic director who has brought the company 50 Helen Hayes Awards, is standing in one of the spacious rehearsal halls. That's one of three, all with 10-foot ceilings. "We can tape out an entire set on the floor. We never could do that before," Schaeffer says, as the cast was assembling in the 2,500-square-foot room for a first run-through of Sondheim's "Into the Woods," which opens tomorrow night.

Behind the scenes, the changes are enormous, mainly because in the old place, there was almost no space behind the scenes. Only 10 performers could fit into the three dressing rooms. (Most musicals have at least 15 performers.) There was one shower. Sometimes the cast had to rehearse in the lobby. The greenroom, where cast members who were not on stage waited, was shared with the orchestra and crew. The sets were built off-site. The Cabaret Series, evenings of show tunes and other songs, was held in the lobby, while technical staff and actors were working a few feet away in the single theater. Parking was dicey, and staffers joked that crossing Four Mile Run Drive to get to the front door was a lot like playing Frogger. Now there is a free 550-car parking garage.

Visiting Schaeffer in the old space could be like watching a slow-motion pratfall. The director would sit on a beat-up red couch, and as he talked he sank and sank and sank, until the cushion underneath him was touching the floor. Now, the bespectacled Schaeffer has all new furniture. While the new place is modern, many of the architectural features are not far in style from what shelter magazines promote in modern kitchens and loft spaces -- the industrial aesthetic.

But most things are entirely different from the old theater, which had the "industrial" without the "aesthetic." There is a grand two-story staircase, rising from the box office foyer to the expansive lobby. The stairs are painted steel with a maple handrail. Behind the staircase are three-story panels made of tiles imported from Holland. Overhead hangs an abstract chandelier of 60 glass globes suspended from a silver plate. The interior was designed by VOA Associates, the firm that did the Chicago Shakespeare Theatre on the city's Navy Pier.

In the main theater, Schaeffer stops and marvels at the ceiling, 29 feet high, double the old one's height. His enthusiasm extends to the six overhead catwalks, and a row of seats called the dress circle, on a balcony level. "These are going to be very popular," Schaeffer says.

The theaters are tight, he says. "It is a square box within a square box, floating on hockey pucks. At $30 a puck. It is built like a soundstage," Schaeffer says, adding that the six layers of drywall will erase competing noises, unlike at the old site. Signature spent $1 million just on acoustics.

In its years in the old 12,000-square-foot space, Signature presented 21 world premieres and specialized in Sondheim revivals. The theater began in 1989 with 136 subscribers; today it has 4,800. In addition to having a comfortable place to see a play, patrons can hang out at the bar for an hour before the show, nibbling on cheese plates or homemade Signature chocolate truffles. A pianist will play in the lobby before the show and after the curtain falls the full-service bar will stay open for an hour.

What Signature has now, more than anything, is light. The exterior glows with a two-story glass facade, and the theater company's name in lights on a column. A dramatic expanse of glass, 14 feet high by 140 feet long, encloses the second-floor lobby.

The actors have elbow room. Now 41 people can use the dressing areas -- four individual rooms for the stars and three shared rooms for the rest of the cast. There are three showers.

The orchestra has its own greenroom. There are three kitchen areas and a proper control room. A costume shop and costume storage area were added.

With the expansion, Signature can have weekday matinees. (Noise from neighboring body shops on Four Mile Run Drive made that impossible in the past.) "Into the Woods" will be performed eight times a week through Feb. 25, Tuesday through Sunday with matinees on Saturday and Sunday.

The second theater will be dedicated to more experimental plays -- new productions and works in progress.

Arlington County invested $5.5 million in the building, a four-story structure that Signature shares with a county library. Signature has the second, third and fourth floors; the library has most of the first floor.

Arlene and Robert Kogod have donated $3 million to the theater, the company announced yesterday, and the box office entryway will be named for them, as will the smaller theater, the Ark. The main stage is called the Max Theatre, named for Maxine Isaacs, who, with her husband, James A. Johnson, was a major donor. The Mead Lobby is named for supporters Gilbert and Jaylee Mead in honor of the late Rob Mead, Gilbert's son. Both couples gave at least $1 million.

Signature had to raise $7.6 million from private sources and surpassed its goal. Gifts to the campaign currently total $10.1 million. Its budget for this season increased to $4.5 million from $2.8 million last year.

Making the transition from the old space to the new will make it easier to raise money from corporations and other donors, Schaeffer says. They tend to like visible projects, and the new lobby gives them a new space for entertaining, he says.

The old space will be turned over to the county for development for other arts groups.