Pataliputra Ruins

The Pataliputra Ruins (華氏城 (パータリプトラ)  遺跡) is a mysterious location in the Toaru Majutsu no Index universe. As the name indicates, it is a castle ruin found in, an ancient city of India.

Index Arc
Stiyl Magnus of Necessarius mentions that Index has been to the ruins prior to the start of the first volume in the timeline alongside the Mont Saint-Michel Abbey, the Vatican Library, Château de Compiègne, and Louvre Museum. There is apparently a grimoire or more sealed in the ruins which cannot be taken away.