Among various factors contributing to autonomous language learners' success, the beneficial role of out-of-classroom activities (OCAs) has been largely neglected. The present case study sought to explore successful language learners' OCAs, their perceptions of the efficiency of these activities, and their purposes for engaging in them. To this aim, four successful teenage English as a foreign language (EFL) learners were selected from an English language institute. Qualitative content analysis of participants' responses to individual semi-structured interviews revealed a plethora of OCAs including Listening to/Watching Authentic Materials, Using Online Media/Materials, and Talking in English to Peers/Parents/Relatives. All of the participants attributed a positive influential role to OCAs in their learning success. Furthermore, among their reasons for pursuing OCAs, the most frequently reported were Personal Interest, Positive Feedback from Teachers/Peers/Family, and Inefficiency of English Classes. The findings suggest that teachers could encourage autonomous language learning by introducing learners to unlimited opportunities outside the classroom.