You have to reach Panvel first. We took an train from Thane to Panvel which took 1 hr and then we took auto from Panvel station to karnala which is appx 12 KM.Karnala is really a cool place and dense forest.You will see greenery at max in rainy season.but if you visit in winter you will see more birds. Accomodation is not available.
You can do trekking till the fort.Trekking difficulty is moderate.It surely tested our physical and mental strength. You have to get down by 6 PM as the sanctuary closes at 6. Overall its a wonderful place.We enjoyed a lot