The phrase "mysterious tower" refers to a tall building or structure that is captivating and enigmatic because little is known about it. Full definition
«Oasis Games is building a strong fall lineup with the acrobatic action and desperate battles of Hidden Dragon Legend, the magical VR puzzles and mysterious tower of Light Tracer and the epic team spaces battles of Fringe Wars. (coin-drop.com)
Thus far the Kingdom of Corona from Tangled, an as yet untitled world from Big Hero 6, Mount Olympus from Hercules, Twilight Town Mysterious Tower, Toy Story and Monsters inc. worlds have been confirmed as new additions. (techradar.com)
Once, in an arid dry landscape, there loomed a large mysterious tower. (popgeeks.net)