The Narmadha Banalingam is a natural stone formed along the Narmada River banks and it is considered a form of Lord Shiva. Devotees believe that Lord Shiva resides in the stone so they worship it by performing abhishekam, offering flowers to it, and chanting mantras to invoke its goodness and blessings on them. The banalingam can be placed in the puja space or beside Lord Shiva's idol or image. Get it from Giri UK.