Kothaligad also known as Peth Killa or Fort of Peth is situated in Ambivili village which is the starting point of the trek. Ambivili and Peth Village are linked so the fort is also known as Peth Killa(Fort). The trek duration for this is about 4 hours approx.
From outside the fort is seems like a chimney on a submarine and is all carved fort in a huge black rock. According to history mostly British have ruled the fort and used it as an outpost.
For more information visit the below link
My blog https://sidsweekendtravel.blogspot.in/2016/10/kothaligad-peth-killa-karjat-trek-that.html