Bhagavan Sri Ramana Maharshi was often said to have had no guru, but he himself considered the mountain-hill Arunachala to be his Guru.
Ramana considered the actual form of Arunachala to be the divine Self, the Pure Consciousness dwelling in the Heart. This is a very strange notion for the rational Western mind, but for those who have tasted Bhakti, or devotional love, it makes complete sense.
Maybe some of you have experienced this: the Guru grips you, magnetically pulls you towards Him (or Her or It) and showers you with His Grace – you have no choice but to Obey. You somehow become convinced that the Guru’s form is itself the Absolute, the Pure Consciousness that Alone Is, and have no choice but to fall at His feet in Loving Devotion.
Ramana wrote very little himself, but of his written works he did write several devotional poetic works effusively praising and thanking Arunachala, his Guru, for bestowing the Guru’s Grace and swallowing him whole.
Grant us the good fortune to fall in Love with Thee!
To experience your Grace!
I am blessed with knowledge of your form!
May I spend my days contemplating your form!
May your Grace continue to pull me towards you and consume me in Divine Love!
May I attain that Great Peace, my Own Very Self, in your Loving Embrace!
You are Arunachala!
You are the True Guru!
You Dwell in me as Me,
Unchanging Pure Consciousness Love!
Om Namo Bhagavate Sri Ramanaya Om
Here is a video in which the above post is read by a devotee: