the citadel – what Saint Teresa calls the ‘interior castle’ – we find another world. Our eyes have become used to the ‘garish day’ outside… the inside of the citadel is much vaster than what lies outside.
Easwaran identifies the citadel with Teresa’s interior castle, arguing that the psycho-spiritual interior is categorically more expansive than external reality, with whole worlds of mind lying between body and Self.
, The Upanishadsthesis