Officials at Mohegan Sun at Pocono Downs, a casino in Plains, Pa., broke ground yesterday on a seven-story, 238-room hotel and a 20,000-square-foot convention center. Plans call for a fitness center, an indoor pool and a bistro serving breakfast and light fare. The Convention Center at Mohegan Sun at Pocono Downs will hold up to 800 people for a dinner and will be able to be converted into a concert venue with 1,500 seats. Construction should be completed by the end of 2013. The property currently offers 82,000 square feet of gaming space, live harness racing eight months of the year, and several dining, shopping and entertainment options.