Surya Siddhanta
तदन्तरपुटाः सप्त नागासुरसमाश्रयाः। दिव्यौषधिरसोपेता रम्याः पातालभूमयः॥
Within this earth-globe lie the seven underworlds inhabited by the snakes (Naga) and demons (asura), which are full of exotic plants and are delightful places.
english translation