Lakhamandal: why is it named so?

Lakhamandal is a famous Hindu temple complex situated in the Jaunsar–Bawar region of Dehradun district, approximately 129–130 km from Dehradun.
As you enter the temple premises, the first structure you notice is a temple built in the Nagara style of architecture, which is widely found in northern India. Most of the remains in the complex have been excavated by the Archaeological Survey of India (ASI).
According to belief, the temple was built by Vishwakarma. It is also believed that the temple was attacked during the Mughal period. Later, during British rule, a wall was constructed at the backside of the temple. In 2007, nearby fields were excavated again by the ASI, leading to the discovery of more remains, including Shiva lingams and kalash.
Inside the complex, there are two idols representing Dev (god) and Danav (evil), placed in the north and south directions respectively. Moving further, one can see a Hawan Kund, which is used during Pandav Nritya, a traditional dance performed by the villagers.
Just above the Hawan Kund is a Shiva lingam associated with Dharmaraj Yudhishthir. It is believed to be the place where the Pandavas assembled for their Rajsabha (meetings). The most famous lingam in the complex is a granite Shiva lingam, in which one can see his reflection when water is poured over it.
It is believed that there are around 1.25 lakh Shiva lingams in the Lakhamandal area, which is why it is called Lakhamandal.
In Hindi, “Lakha” means many, and “Mandal” refers to a group of temples or lingams (as per Wikipedia and local belief).
The journey through the Lakhamandal temple complex does not end here. It is believed that the site spreads across an area of 8–9 km, much of which is yet to be excavated. There is still a lot to explore in the surrounding areas, but due to bad weather conditions, we could not visit further.
P.S.: I hope this information is helpful. For a deeper understanding, please do refer to other reliable sources as well.