MARBLEHEAD – The Marblehead/Swampscott YMCA has operated out of two buildings since it opened in 1859.Saturday at 6 a.m. the "Y" will open its state-of-the-art, 90,000-square-foot, $15 million third building on a hilltop on Leggs Hill Road, which just might be a fitting present for the Y’s upcoming 150th anniversary.The new building features a climbing tower, a cafe, a physical therapy room, baby-sitting, gymnastics areas, a gym, four Boston Ballet School studios, two aerobics studios, squash courts, conference rooms, a multi-purpose room and a pre-school. The pre-school opened Thursday. The physical therapy center is run in collaboration with the Shaughnessy-Kaplan Rehabilitation Center in Salem.The new Y is one of the largest YMCA buildings in New England and was financed by one of the largest YMCA fund-raising campaigns in the region as well.The first floor will soon offer two swimming pools. One is about three times the size of the pool in the Pleasant Street building that the Y has occupied since 1910. The other one is even larger. Those pools are "a few weeks behind," according to Executive Director Paul Gorman, and are scheduled to open in January. An outdoor pool will be finished next spring.It hasn’t been easy getting to this point. Construction began two years ago and fund-raising began six years ago.Thursday Gorman called the building "the first significant project Marblehead and Swampscott have done together and larger than either of the high schools they built recently.""This should be seen as a community center," he said.With a 250-space parking lot, it may not just be a center for Marblehead and Swampscott. "We get a lot of people from South Salem and don’t tell anyone, but we may even get a good group from Lynn as well," Gorman said.YMCA membership has grown 50 percent in the past two years, from 3,000 to 4,500, and Gorman hopes it will grow even more.Meanwhile the Y is still looking for the last $600,000 it needs to raise. Donations may be made online at www.northshoreymca.org or by contacting the Y at 781-631-9622.