Ravana was an ardent devotee of Shiva and there are numerous
stories associated with Shiva, Shivling and Ravana. In the Uttara Khanda of the
Ramayana it is mentioned that Ravana always carried a golden Shivling. Ravana
had also composed the famous Shiva Tandava Stotram.
Where Ravana went he carried with him the golden Shivling
for his worship. He used to create a pedestal of sand and place the Shivling
on it. He then used to worship it. Puja was performed with incense and fragrant
flowers.
Golden Shivling is intended for constant worship. Ravana
worshipped it from the desire of sovereignty.
It is described in the Tantric texts that a golden Shivling
should be worshipped when any one desires sovereignty.
It is also believed that worshipping a Shivling made of gold
grants wealth (Sripadam).
Source – Elements of Hindu Iconography – Vol II. Part 1 – by
T. A. Gopinatha Rao.