Comcast Center, also known as the Comcast Tower, is a skyscraper in Center City, Philadelphia. The 58-story, tower is the second-tallest building in Philadelphia and in the U.S. state of Pennsylvania (after the Comcast Technology Center), as well as the twenty-third tallest building in the United States. Originally called One Pennsylvania Plaza when the building was first announced in 2001, the Comcast Center went through two redesigns before construction began in 2005. Comcast Center was designed by Robert A.M. Stern Architects for Liberty Property Trust. In early 2005, the final redesign and its new name—the Comcast Center—were unveiled. The building is named after its lead tenant, cable company Comcast, which makes the skyscraper its corporate headquarters. Leasing , Comcast takes up 89 percent of the building. The building features retail and restaurant space and a connection to the nearby Suburban Station. In Comcast Center's lobby is the Comcast Experience, which is a high-definition LED screen that has become a tourist attraction. Designed to be environmentally friendly, the skyscraper is the tallest Leadership in Energy and Environmental Design (LEED) certified building in Philadelphia. History Planning (1999–2004) In 1999, class-A office vacancy in the city was at 6.6%, leading developer Willard Rouse to envision a new tower. Eventually the developer settled on the location where he constructed this building, a , $288 per square-foot parcel owned by Equitable Life Assurance Co. In 2000, the architect and Driehaus Prize winner Robert A. M. Stern began working on a design for a skyscraper being planned by Liberty Property Trust in Philadelphia. In 2001, Liberty Property Trust announced its plan to build the 52-story One Pennsylvania Plaza in Center City. Anticipated US$400 million, One Pennsylvania Plaza was to be and made of kasota stone similar to the Philadelphia Museum of Art. The site for the future skyscraper was situated at 17th Street and John F. Kennedy Boulevard, a site occupied by a building that housed the Defender Association of Philadelphia and a parking lot. Demolition of the building began in 2002 and ended in 2003. Cable company Comcast had been looking for possible new headquarters space in anticipation of the end of its lease in Centre Square in 2006. Comcast was looking for more than of office space and developers were actively courting the company for their developments. Comcast was the only employer in the city with major expansion plans at the time. Comcast was