Ashtavakra Gita(Ancient hindu philosophy poem) : It really opened a new dimension of thinking for me. It's main message of identifying yourself as the witness consciousness is quite trippy and the sanskrit used is quite powerful. It plays around with the concepts of soul , karma and concept of non-duality in quite radical ways. I found it quite an empowering way of going about life, one can only imagine how it must have felt for the original author/s who discovered it as an "insight" on the reality of life. Such people nowadays would be called delusional though.