According to Kashi Khand, Chapter 69, the place where Lord Shiva wore the skin of Gajasur after slaying the latter, was called Rudra Vasam. (Kindly refer to Krithi Vaseshwar).
Once the Lord, in his form as Krithi Vaseshwar, was sitting alongwith Goddess Uma Devi when Nandi offered his prayers and stated that there are 68 places of worship dedicated to Lord Shiva in this holy place. Various idols/Shiv Lings have been brought from several other places by Nandi and installed in Kashi.
From a place called Rudra Mahalayam, Rudreshwar has appeared in Kashi in form of a Ling. Devotees who worship Rudreshwar are certain to reach Rudra Lok (heaven). A person who performs pooja of Rudreshwar Ling in Kashi is sure to be venerated as Lord Rudra.
In another reference, (Kashi Khand, Chapter 97), Goddess Parvaty wanted to know about the various Shiv Lings and deities at several places in Kashi and Lord Shiva was pleased to narrate about such deities.
Lord Shiva narrates about a pond called as Rudravasam where devotees can find Rudreshwar. A devotee who worships this Lord will derive the benefits which would normally accrue on worshipping one crore Rudra Devas.
Kashi Khand mentions Rudreshwar at two locations one at Rudravasam (in the vicinity of Krithi Vaseshwar) and the other near Tripureshwar (Tripura Bhairavi). While the first Shiv Ling no longer exists, the location below pertains to the second Shiv Ling.
On the day of Chaturdasi (fourteenth Day after Amavasya or Poornima) when Ardra (Tiruvadirai) star conjoins, this period of time is very very auspicious. If a person takes bath in Rudra Kund and performs pooja of Rudreshwar, he will certainly reach Rudra Lok, even if he dies in any place other than Kashi. (Of course, death in Kashi will ensure a place in Heaven, that is implied). While Rudra Kund is not in existence, devotees may take bath in River Ganga.
For ready reference, Chaturdasi Thithi falls twice in a month and Ardra is one of the 27 stars. Devotees have to watch out for this combination in the almanac (Panchang). This combination can occur once in an year. In the year April 2009 to March 2009, devotees saw this combination on 21-07-2009. During the last year (April 2008-March 2009) this combination occurred on 10.01.2009.
Since Kashi Khand has attached so much importance to this combination, it is worth going through the Panchang.
LOCATION OF RUDRESHWAR
Rudreshwar is located at D.5/21, near Tripura Bhairavi (D.5/24). Devotees can approach Tripura Bhairavi Temple by travelling upto Dasaswamedh Vishwanath Gully by rickshaw. After entering the Gully, immediately there is a right turn. Devotees may take that right turn, walk for about 100 yards and ask for Tripura Bhairavi Temple. Just after the temple, there is a left turn and Rudreshwar is located on the first door on the right side, inside a house.
Rudreshwar is a huge Ling and the residents of the House permit devotees to worship this Ling.
TYPES OF POOJA
The deity is situated inside a house. However, they permit devotees to perform pooja.