This small park near San Francisco’s financial district is the birthplace of Twitter. According to Jack Dorsey, Twitter’s co-founder (and, later, founder and CEO of Square), he first shared the idea for everyone’s favorite status-sharing service with two of his Odeo co-workers while on the slide in this park in 2006. Shortly thereafter, the idea was fleshed out and a prototype built, which served as an internal communications service at Odeo. The following year, Twitter, which Dorsey originally wanted to call Stat.us, was formally spun off as its own company by founders Dorsey, Evan Williams and Biz Stone. Of course, if you visit the park, be sure to tweet out a picture.