As part of the broader secularizing policies of the early Turkish Republic, Law 677 closed all Sufi lodges in Turkey on 30 November 1925. While 127 lodges in Istanbul were formally secularized and transferred to the state as museums, nearly all were subsequently abandoned, looted, or destroyed until the 1990s due to the lack of state funding. One notable exception was the shrine of the fourteenth-century saint Karacaahmet in Üsküdar, Istanbul. Karacaahmet was widely known as a healer, particularly associated with mental illnesses, and multiple shrines are attributed to him across Anatolia and the Balkans. The Üsküdar shrine is distinctive both for its location within Istanbul's oldest and largest cemetery and for housing an additional shrine dedicated to Karacaahmet's horse. Built in 1539 by Gülfem Hatun, the complex never functioned as an institutional Bektashi lodge (tekke). As a result, it remained officially classified as a museum by the secular state, while simultaneously constituting an invisible religious space in terms of Alevi identity and practice. This paper examines how Alevi actors sustained, reclaimed, and gradually Alevized the shrine from the mid-1940s onward. Drawing on previously unexamined internal archives of the Istanbul Museum Directorate of Shrines—closed to public access—it traces how individual Alevi initiatives of maintenance and caretaking evolved into institutionalized collective action with the establishment of one of the first Alevi associations of the Republic in 1969. Through close cooperation with the Istanbul Museum Directorate of Shrines, these actors were able not only to preserve the shrine but also to construct a cemevi on the site in 1990 and to protect it from later interventions by Islamist municipal authorities under Recep Tayyip Erdoğan. By foregrounding Karacaahmet as an inconspicuous yet sustained place of worship, this paper contributes to the study of invisible religious spaces.