Arnala Fort lies in the village of Arnala in Vasai of Thane District. This fort, also known as Janjira or the Island fort, is on Arnala Island near the mouth of Vaitarna River. It was originally constructed under the patronage of Sultan Mahmud Begda of Gujarat in 1516. In 1530, the fort was rebuilt by the Portuguese. The brave Bajirao Peshwa - I conquered the fort and modified it in 1736. Arnala Fort came under the rule of British in 1781.
The place holds vital importance in the history of India's freedom struggle where the first Salt
Satyagraha was held. There is a large hexagonal fresh water reservoir inside the fort. There are temples of Ambakeshwar, Goddess Bhavani, Lord Shiva, and tombs of Shahali and Hajjali inside the fort. The 'paduka' or sacred sandals of Shrinityanand
Maharaj are housed in a dome on the eastern face of the fort. The solid stone doorway is adorned with pictures of tigers and elephants.