Worship of a Shivlinga is measured as the ultimate worship for Lord Shiva devotees. Worshipping Lord Shiva in any other form takes secondary prominence. The importance of the Shivlinga is that it signifies the magnificent light that is the indication or identity of Lord Shiva. This light or flame is solidified and makes the Shivlinga.
This light of Lord Shiva exists in all Shivlinga forms and is important in different places all over India. These are famously known as Twelve Jyotirlingas. Here is an ancient shloka that lists the twelve Jyotirlinga temples. One, who recites this shloka regularly, gets rid of all the sins committed in the previous 7 births.
Ujjayinya Mahakalam Omkaramamaleswaram ||
Paralyam Vaidyanathancha Dakinyam Bheema Shankaram |
Setu Bandhethu Ramesam, Nagesam Darukavane||
Varanasyantu Vishwesam Tryambakam Gautameethate|
Himalayetu Kedaaram, Ghrishnesamcha shivaalaye||
Etani jyotirlingani, Saayam Praatah Patennarah|
Sapta Janma Kritam pApam, Smaranena Vinashyati||"
The location of the twelve Jyotirlinga temples are spread across the length and breadth of India. Two are on the seashore; three on riverbanks, four in the mountains and three are situated in villages.
Here is the list of these twelve temples with information on each individual temple in brief.