Task-based research has shown the benefits of using tasks in various instructional contexts across different age groups. Although task-based language teaching promotes language learning through authentic real-world tasks, previous research has mainly used controlled pedagogic tasks. The current exploratory, intact-classroom, multi-case study examined the extent to which 13 Korean adolescent learners of English used and learned new English lexical items while carrying out an uncontrolled, real-world, multimodal, video-creation task. It further investigated students' perceptions of performing such a task. Target items included 93 English lexical items that appeared in realia at a historical site in Korea. The video-creation task was carried out over 5 days and included pretask planning, a field trip to the Korean historical site, and creation of a travel guide video for the site in a computer lab. Students' interactions were recorded digitally. Results revealed that the degree of target-item production varied by participant, but overall target lexical items were not greatly used by students. Students' perceptions of the benefits of the uncontrolled, real-world task seemed to relate to task-as-process, which was directly influenced by learner-generated workplans. Pedagogical implications for designing and implementing real-world tasks requiring task performance inside and outside of the classroom are discussed.