The Mundeshwari Devi Temple, Bihar - one of the oldest Hindu temples in India!!

625 CE Nagara style architecture of the Hindu temple,Bihar, en.wikipedia.org.

The ancient Mundeshwari Devi Temple (also spelled as Mundesvari) of Kaura in Kaimur district, Bihar  is dedicated to Lord Shiva and his consort Parvati. Located on the Mundeshwari Hill (608 feet tall), it is believed to be  one of the oldest  functional Hindu temples in India. Its date of construction goes back to 635 CE as per  inscriptions in the temple.  But the plaque fixed by the ASI says it is 625 CE. Under the management of  the Archaeological Survey of India (ASI) since 1915, it is centrally a protected monument .

Built in the Nagara style of temple architecture, the temple has an   an octagonal plan which is a rare one. In the Garbagriha - sanctum, there are main deities  the Devi Mundeshwari and Chaturmukh (four faced) Shiva lingam.  The temple tower or shikara is missing, however, a roof is built as part of renovation work. At the entrance to the temple, the door sides carry  carved images of Dvarapalas (sentinels), Ganga, Yamuna and many other deities. The unique feature is there are  doors or windows on four sides and small niches for the statues in the remaining four walls. There are  also niches on the interior walls with  bold moldings  carved with vase and foliage designs. 

Mundeshwari Devi Temple, Bihar .google.com/

 Yet another fact of considerable interest here is in the sanctum Shiva's consort  enshrined in a niche is the main deity, not withstanding the fact that the Shiva lingam is at the center. The main presiding deity is  called Devi Mundeshwari  and she has  ten hands holding symbols riding a buffalo, attributed to Mahishasuramardini. Also present in this temple are the idols of other deities in the Hindu pantheon such as Ganesha, Surya and Vishnu. 
A  sad commentary is many of the  stone structures  are damaged beyond redemption as one can see  many stone fragments strewn around the temple.  The reason for the damages is not clear and  temple records do not attribute the damage to Muslim invasion.
During the Ramnavami, Shivratri festivals, this temple is over  crowded. So is during the main  annual fair (mela)  that coincides with the Navaratri festival. A fact worthy of mention is the conduct of temple rituals. Unlike other Hindu temples, here  rituals and worship have been performed without a break since 108 AD. The worship of Shakti in the form of Devi Mundeshwari in the temple  suggests due importance is given to tantric cult of worship, which is practiced in  states like Kerala.

The Archaeological Survey of India undertook restoration work to preserve this protected monument.  The works  was focused on the removal of soot from the temple interior using special chemicals, repair of damaged image of deities and, importantly, cataloging and documentation of scattered fragments for later reuse. They also introduced  solar powered lighting besides display of  antiques and  additional provision for  public amenities.  A sum of Rs 2 crore was earmarked for the restoration work by the Government of Bihar. 

There was a proposal to develop this ancient temple on the model of Vaishnavo Devi temple of Jammu and Kashmir. Incidentally this 1900 - year old Hindu shrine is being looked after  by one Azeemuddin, a Muslim, for the last many years. Historians believe this temple came up in the Shaka period that predated the Gupta period 320 AD.

Mundeshwari Devi Temple, Biharwww.google.com

The temple is on the Kaimur plateau near Son River (and Survuwara (suvara) river) and there are many archaeological relics on the Mundeshwari Hill. This temple can be reached by road from
Patna, Gaya, or Varanasi. The nearest railway station is at Mohania - Bhabua Road railway station from where the temple is 22 km by road.
 https://en.wikipedia.org/wiki/Mundeshwari_Temple
 http://www.bihartimes.in/news08/Jan/19jan3.html