The theertam opposite the Mahakaleshwarar temple is known as Koditheertham & it is said that the colour of the waters of this theertham keeps changing. The Moola lingam is very small & is located underground.
The lingam in the top level is called Ongareshwarar. The Kali Devi who gave darshan to Vikramaditya is known by the name Harasiddhi Matha. There once lived a brahmin in Avanti, who had four sons, who were great devotees of Lord Siva. Dushanan, a demon was giving trouble, disturbing all good & religious activities. The brahmins from all over the land gathered with the four sons & performed pooja to Lord Siva. The spot where they had taken mud to make the Lingam had become a huge pond. When Dushanan came to disturb their pooja, Lord Siva rose from this pond as Mahakaleshwarar & destoryed Dushanan. On the request of the brahmins, Lord Siva gave darshan to devotees at this sthalam, one of the Jyotir Linga sthalams.