Moheshkhali is a remote island that is located several kilometers apart from the main town of Cox'sbazar. You have to reach that island by boat/trawler or other water vehicles, no alternate ways. It will take you around 15-25 minutes to reach the island. If you are using a trawler, it will take you 65 taka for the lift. The trawler journey is exciting one, and I have enjoyed the ride. Hope you will do so.
I have a friend, who was in search for an island from bangladesh which has mountains/hills. Finally i got one, and this is Moheshkhali island. It has numerous number of small hills through out the island. So if you like to enjoy the beauty of island and hills from Bangladesh, then moheshkhali is the only option for you(so far my knowledge is). You'll find lots of pagodas at the top of the hills. Most of the pagodas are same in shape and size and color. From my observation, most of them are made from brass.
The hills are covered with green plants. It can be grass, bushes, planted trees by human, or natural trees. The hills which are near to the shore will be better if you get top on those. You can easily see the sea, or the moheshkhali channel from there. Its a tremendous feelings when you'll be there, trust me.
If you are lover of dry fishes(shutki), then you may want to visit some villages to see how the dry fishes are processing. For your information, most of the dry fish supply comes from this part of the country. So don't miss your opportunity. By the way, I don't like dry fish, its pungent smell is enough to make me feel sick.
The island has lots of varieties mangrove trees at the shore. The green shore is a nice view from the boats. You can have a boat, and enjoy a jaunt at the channel for a while. Remember, this is a lovely island, where you can pass your whole day. I'll recommend you to take foods with you if you are planning to pass the whole day there.