Shaped by water and enclosed by the Prenestini, Ruffi, Simbruini, and Lepini mountains, the Aniene Valley reveals a landscape of remarkable complexity, where nature and history intertwine in a continuous process of transformation. Stretching between Rome, Tivoli, and Subiaco, this territory unfolds along the seventy kilometres of the Via Tiburtina, preserving ancient and modern traces of human presence and a long-standing dialogue between people and the environment. This guide offers a renewed interpretation of the Valley through interdisciplinary contributions, highlighting sacred spaces and a living, fragile landscape - a threshold between the Ager Tiburtinus and the mountains, to be rediscovered with a more attentive, mindful gaze.