The tallest building ever intentionally demolished was the 47 floor Singer Tower in Manhattan, the only other tall buildings ever to be taken down are the World Trade Center by terrorists. Relatively little thought has been given to demolition of skyscrapers, especially in dense urban areas where they reside.
The song sometimes called the "hippie national anthem" can be found in all kinds of places. It's been used on The Simpsons and in Forrest Gump, recorded dozens of times by the likes of The Kingston Trio, The Dave Clark Five, Jefferson Airplane, The Staples Singers and the Carpenters (twice). You may have even heard it in a Walmart commercial a few years ago.
The song has gone by a few different names: "Let's Get Together," Everybody Get Together." But the best-known version is called, simply, "Get Together." It was recorded by The Youngbloods in 1967 — the same year as the Summer of Love, where it would become a constant presence.