The Jain temple at Achalagadh was built by Saṁghavi Sahasā, grandson of Ratnashah (who was the brother of Sheth Dharnashah who built the Ranakpur shrines. He installed a very heavy metal idol of Lord Rsabhdeva as the main deity weighing 120 maunds (approx 4500kgs). The consecration ceremony took place on Falguna Shukla 10 in 1509AD with the blessings of Acharya Shri Jayakalyānasuri. There are inscriptions which suggest that the image and possibly the shrine was the work of artist Depā of Arbudā. It is a Chaumukha temple (four idols facing the four cardinal directions). Sahasā received inspiration to built the temple from Jain monk Sumatisundara.
The fort is believed to have been constructed/renovated by Rana Kumbh .
The temples are built on a high peak of the Abu mountains. There are various bronze and metal idols in the temple weighing upto 1444 maunds in total which are nowhere to be found. Some believe that the temple was created at such a high elevation so that the local king could pay his respects to the Jinas from the balcony of his palace.
At the foothills is the Shrine of Achaleshvara Mahādeva which is an ancient Hindu site. The Hindus believe that Achaleshvara Mahādeva is the superintendant deity of Mount Abu.
Yogiraj Acharya Vijayshantisuriswarji performed many austerities at Achalagadh and he departed from this world at this place. There is a memorial shrine dedicated to him at the final place of austerities and ultimate departure from this world.
References:
1. Internet
2. Some Photos from World Org Website