CLEARWATER — The Church of Scientology has purchased and remodeled dozens of buildings since it established its spiritual headquarters here 37 years ago. This weekend, it will open yet another.

But this one — a seven-story behemoth with more than 300,000 square feet — is being touted by the church as a game changer.

On the fifth floor, Scientology will make available to its members for the first time a "Super Power'' program developed in the 1970s by church founder L. Ron Hubbard.

Hubbard called Super Power one of his greatest discoveries. He said Scientologists would develop special abilities, enabling them to reverse social decay and "create a new world.''

The church kept details of the program under wraps until it could build a proper venue to deliver it. Now, after 15 years of on-and-off construction — and controversy — the building finally is finished.

Scientology says it's the most important project in its 59-year history. And indications are it will represent another important first for the church in Clearwater.

Recruiting new followers will be emphasized, it appears from a Tampa Bay Times review of church publications, internal memoranda and construction plans submitted to the city.

Proselytizing has been a common activity at Scientology's other churches, including its prominent facility in Ybor City. The Clearwater campus, Scientology's spiritual center, has focused on delivering services, not recruiting newcomers.

But much of the new building's ground floor appears designed to do just that. The primary public entry, on the northwest corner, opens into a "grand lobby,'' a three-story atrium with statuary and other exhibits depicting Scientology beliefs and practices.

A visitor then would move toward the center of the building, into a large area with more displays, films and promotional presentations. Clustered in circles in a museum-like setting, these displays appear to explain associated Scientology organizations and the social efforts Scientologists support.

The church has said little about the building's features, apart from Super Power. Church officials did not respond to Times requests to tour the building and ask questions about its uses, but even most Scientologists will not have seen it before a ribbon cutting Sunday afternoon.

As many as 10,000 church members are expected to attend the private event, as well as two other nighttime gatherings today and Saturday in a huge tent erected by the church just south of the new building. The church has not announced the purpose of the evening events.

The building's seven floors present widely divergent uses.

In the basement — a rarity in Florida — are huge kitchen and dining areas. The second and third floors contain offices and Scientology course rooms for training. The upper floors have more than 300 small rooms for "auditing," Scientology's core counseling practice. An auditing session usually lasts about an hour and can cost $1,000.

Large spaces on floor five are dedicated to the Super Power program, a series of 12 "rundowns'' that combine auditing with drills involving machines.

Participants will be spun on a gyroscope-like wheel, spend time in a sound chamber, sniff vials emitting fragrances, experience changes in gravitational pull. The aim: sharpen what Hubbard called man's 57 "perceptics'' — sight, smell, taste, touch, blood circulation, depth perception, solidity, awareness of awareness.

On the sixth floor is another intriguing feature: a circular running track, its radius: 74 feet. Scientologists will go around it until they have a personal moment of enlightenment called a cognition. Hubbard called this the "Cause Resurgence Rundown.''

The church has not said whether it plans to invite the public to tour the structure, known as the "Flag Building," now the centerpiece of the church's Flag Land Base in Clearwater.

Construction plans at City Hall suggest the church filled the building with rich amenities and high-grade materials, as is its custom with other projects.

Despite that luster, the building will debut Sunday amid considerable controversy. Much of it centers on allegations that the church purposely delayed construction to keep alive the building's fundraising drive.

The church started raising money for the Super Power complex six years before construction began in 1998. After the shell was completed, the church halted work. It said little as to why.

After three years of inactivity, the city started imposing a $250-a-day fine for code violations. But the church didn't resume work for three more years.

In 2011, the church indicated the building was nearly complete. It paid the city a cumulative fine of $413,500 and got a certificate of occupancy.

Church spokeswoman Karin Pouw told the Times then that church leaders had stalled construction because they had underestimated how fast Scientology was growing and needed to replan parts of the interior.

A Times analysis of the fund drive determined the Super Power campaign had brought in at least $145 million by 2011 — substantially more than the $100 million project cost often cited by the church.

In January, former Scientologists Rocio and Luis Garcia of Irvine, Calif., filed a fraud lawsuit against the church in federal court in Tampa, alleging the church prolonged the project "as a shill'' to continue raising money.

The Garcias contributed more than $340,000 to Super Power before leaving the church in 2011. The church has called their suit frivolous.

In May, members of Pinellas Property Appraiser Pam Dubov's staff toured the Flag Building and confirmed all floors will be used for religious, tax-exempt purposes.

The church had paid taxes on the property during years of stop and go construction. And Scientology pays property taxes on portions of some of its other holdings — spaces such as hotel rooms and restaurants used for commercial, non-religious purposes.

This newest building, valued by Dubov's office at $84 million, is fully off the property tax rolls.