Despite the strife going on outside, this city is a safe zone, and you won't have to worry about encounters here. To get planes flying again, you have to clear the radio tower. Be aware that you'll be locked in when you enter, so make sure you're fully stocked on recovery items before proceeding.
1st floor: As soon as you enter, you'll be trapped inside until you defeat the boss on the top floor. Not much else here - there are vending machines, but they're out of order.
2nd floor: Besides the trash can encounters that are hopping up and down, the ceiling will also randomly crumble, damaging the party. Still no bosses or events of note here. After defeating Raul and Inc, you can enter their green room and read Inc's journals on the bookshelves.
3rd floor: As soon as you enter, you'll be inflicted with the Tired status, which will halve your movement speed and cause you to take damage as you walk. Near the recording booth to the left is Deja Voodoo user of Heavy Stereo - talk to him to start a battle, and after you win, your movement speed will return to normal and you'll be allowed access to the 4th floor.
In addition, you can now fight an additional boss. A man in the cafeteria who will give you a Chocolate Bar if you talk to him. Bring it to the little girl on the lower-left side of the second floor to start a battle. Afterwards, you'll receive a Sunlight Remedy, and the trash cans as well as the crumbling ceiling will no longer attack. Be warned that this event can not be triggered after defeating Inc & Raul, and if you leave Sundarbans with the chocolate bar, you'll receive +1 bad karma.
4th floor: Fight your way through the zombies until you reach the Slaves to Fate members, Inc & Raul. Once they've been defeated, the planes will start flying again, and you can depart Sundarbans using the airport. You can also check the nearby bookshelf containing Inc's journal for a bit of backstory.
Weak, weak, weak. Unless you haven't been keeping track of your HP with the damage from the falling ceiling, these guys won't be a problem.
MINI-BOSS: Deja Voodoo
Has a lot of attacks that inflict Stop. Low HP, so take him out quickly before he gets the chance to use them.
OPTIONAL BOSS: Alice
Defeating her will result in an instant Game Over. Use Brainstorm to end the battle or go after Sevendust.
OPTIONAL BOSS: Sevendust
Doesn't attack, but attacks don't work well against it, either. You can end this battle with the Brainstorm command. If you really want to defeat it, use status effects such as Bleeding, but you won't get EXP or drops. However, you will get a Badge of Honor for winning this way.
Same as the ones you've encountered everywhere else.
Same overworld sprite as the regular zombies, but they move a lot faster.
Your party will start this battle with the Darkness status effect. Status effects are going to be more of a problem than damage here. Be especially careful of the Stun Senses attack, which makes it near-impossible to land hits and halves your stats.
Inc & Raul
Supports Meatloaf with machineguns. Will use medicine to heal if you attack them.