Purpose: The objective of this study was to gain insight into the experiences of nurses who provided care for patients with COVID-19 in residential treatment centers (RTCs) during the pandemic. Methods: This study adopted qualitative methodology and conducted in-depth interviews with seven nurses from three residential treatment centers between July 11 and August 27, 2022. Inductive content analysis was employed, which consisted of data understanding, open coding, grouping, categorization, and abstraction. Results: Three themes and eleven subthemes were extracted from the data. The themes identified were "A struggle from beginning to end," "Unexpected challenges," and "Insecure system like a house built on sand." Nurses encountered difficulties in all aspects of the center's operations. Frequently, they were required to perform tasks outside of their responsibilities. During this process, nurses encountered difficulties due to unexpected challenges. Conclusion: Nurses encountered significant challenges in providing care to patients in an under-resourced and disorganized environment. They were compelled to assume diverse responsibilities for managing the center owing to the lack of clear protocols and guidelines and frequent changes. Unlike nurses in hospitals, nurses in RTCs spend a greater proportion of their time on non-medical issues, which can lead to emotional exhaustion. Based on these findings, it is imperative to establish clear guidelines and protocols to effectively run residential treatment centers in the future.