While some students are enjoying days at the park or at the beach, forty middle school students are in a classroom solving challenging mathematics problems. The second Math Camp for middle school students was offered in 2013 at a western university for students from local school districts. For three days, these students met from 10 a.m. to 3 p.m. to enjoy mathematics and to work hard. Students persevered in finding solutions, sharing different ways of thinking, providing logical arguments, and presenting solutions for whole-group discussion--all practices that align directly with the Common Core's Standards for Mathematical Practices (CCSSI 2010). These standards urge educators to provide experiences that help students develop deeper understanding. What follows in this article are examples of rich problems related to triangular numbers, students' ways of thinking about them, and the teachers experiences with the students during the camp. An activity sheet is included as a resource for teachers.