Recently I visited this fort and found that its is relatively easy for even inexperienced trekkers.
Accessibility- It is very near to panvel station.from panvel(mumbai, Maharashtra) S.T stand you can easily get bus or rickshaw. Karnala fort is 10km from panvel station .
Attractions- First and foremost attraction is bird sanctuary.There are many types of birds(around 140 types)but if you want to see them you should reach there at 5.30am, Second is Karnala fort.its very ancient fort and easy to climb
Hotels and accommodation- It is one day trek and at the bottome of this fort there is one small hotel where you can get food.
Safety-Since its easy trek you can go ther with only good griped shoes, Water bottle(2 liters), Snack with you.