Tracy Campion of Campion and Company Real Estate is the exclusive broker for these boutique homes.

Twenty-Five Beacon is beyond spectacular. It is the epitome of luxury. The distinctive six-story Beacon Hill building next to the State House and overlooking Boston Common has been converted to six amazing residences, and two of them have an au pair suite.

And the amenities are extraordinary. A wine cellar/tasting room, paneled in cherry, features six individual 120-bottle cabinets as well as a wet bar. A nearby fitness room with state-of-the-art exercise equipment boasts a floor-to-ceiling mural of Fenway Park and a mirrored wall.

A live-in concierge is available around the clock and will provide valet services for the 14-car underground parking garage.

Tracy Campion of Campion and Company Real Estate is the exclusive broker for these boutique homes.

Sea-Dar Real Estate and CNW Capital Partners, the developers of 25 Beacon, engaged CBT Architects and Reza Nouranian Design to create elegant interior spaces that would appeal to the finest tastes. Sea-Dar Construction was the general contractor.

Of the six condominiums, only two are available, Units 2 and 4. Last week, the penthouse with an au pair suite sold for $11,833,303, and Unit 3 sold for $8,850,000. Units 1 and 5 are expected to close shortly, said Jean Abouhamad, development manager.

The developers acquired the building along with two townhouses on Mount Vernon Place, directly behind 25 Beacon, about three-and-a-half years ago.

Completing the technical engineering for the underground garage and securing the necessary permits was a very long process, said Abouhamad.

The exterior was completely restored to its original grandeur, and the attention to detail and the quality finishes further extended the length of the construction.

It has been a labor of love, he said, noting this is the largest project he has undertaken on speculation.

Last week the development team showcased the property to the brokerage community, and the homes sparkled.

Nouranian, principal of RND, staged Unit 4 with custom-designed furnishings, including a long dining table, a glass-topped coffee table with sand, and antique chair replicas. Joseph Carroll of Carroll and Sons Gallery loaned artwork.

Unit 4 is listed at $9,350,000, said Campion.

Granite steps ascend to the columned recessed entry, which opens into a splendid foyer, tiled with mosaic marble bordered by a Greek keystone pattern. A mirrored wall expands the sense of spaciousness, and the other walls have custom paneling that compliments the appliquéd ceiling moldings.

Next to the custom-designed wood concierge desk is a hallway that leads to the direct-access elevator.

On the fourth floor the elevator opens into a gallery that extends the full 132-foot-length of the home, from the living/dining room to the master bedroom suite.

Paneled wainscoting, wide-plank white oak flooring and recessed lighting in the gallery transition into the grand living/dining room, which is 32 feet wide. The ceiling soars, and the front windows offer stunning views of the Midtown towers, Boston Common and the Back Bay skyscrapers. Here the white oak flooring is laid in a chevron pattern.

Between the two other windows that look out to the State House lawn is an especially designed gas fireplace of mottled gray Turkish marble.

A custom-designed chandelier is suspended above the long dining table.

Next to the living room is a stunning gourmet kitchen with honed dark gray jet mist schist that wraps around the room. High-end Gaggenau appliances include a gas cooktop, oven, refrigerator, wine fridge and dishwasher. The microwave is by Wolf.

The largest counter slab with a rectangular sink delineates the breakfast area surrounded by custom cabinetry with painted glass fronts.

This area continues into a family room with another fireplace with a surround of pale gray marble. Like the kitchen, the flooring here is quarter-sawn and rift white oak. A wide doorway faces the elevator and a stylish powder room with a limestone-topped vanity and accent wall.

Double doors separate the main entertaining spaces from the private quarters. On one side of the corridor are stairs and a tiled laundry room, equipped with a side-by-side LLG washer and dryer and Caesarstone counters.

Two bedrooms are on the opposite side, each with an en suite bath. One of the baths, which has a tea-for-two tub and a beige marble-tiled floor, also can be accessed from the hallway. The other bath has a glass-enclosed shower and ocean gray Marmara marble floor.

Beyond these rooms is the master suite. A large dressing room filled with custom closets and a dressing table lies opposite the lavish master bath with a radiant heated floor. A stand-alone soaking tub sits between two tall windows, and on either side of the room are especially designed single marble-topped vanities with storage.

Two large glass box-like enclosures with partially frosted walls are aligned with the vanities. One of them holds the toilet; the other, the shower, which has a wide rain showerhead.

The residence concludes with the master bedroom, a retreat unto itself, with windows on three walls. Quarter-sawn and rift white oak flooring, crown molding and a low chair rail are subtle finishes.

Unit 2, listed at $10,500,000, has the same floor plan as Unit 4, but includes an au pair suite on the lower level of the building. The 413-square-foot space has a compact kitchen with stainless steel appliances and a laundry closet and a large bath with a combination tub/shower.

In addition, the second-floor residence has 12-foot ceilings adorned with crown molding. Outside the windows are wrought iron balconies.

(Unit 4 has an outdoor balcony outside its family room and second bedroom.)

Originally, the granite and brick Colonial Revival building was designed to serve as headquarters for the Unitarian Universalist Association. It stood on land once owned by John Hancock. William E. Putnam Jr. and Allen H. Cox designed the building in 1925.

In 2014 it sold all of its Beacon Hill properties to establish new headquarters in the Fort Point/Innovation District.

By all accounts, the restoration of 25 Beacon and its conversion to condominiums surpass anything one could imagine.