Abandoned town

Abandoned towns are giant walled off areas with only one entrance. Iron doors that have an entrance pressure plate but not an exit pressure plate so if you go into an abandoned town you are trapped there. Abandoned tons are more like cities, they are filled with small wooden houses that are spread out in a mazelike pattern. There are only five per server.

Castle
After finding your way through the maze to the back of the town you will find a giant castle with iron doors. Once you go in the castle you are locked in. In the middle of the entrance hall are more iron doors, you must find the lever that operates them to enter the basement. In the basement is a coffin.

Boss fight!
Mine the lid off the coffin and a Vampire will jump out, it is the boss of an abandoned town. It has a few unique attacks:

Drain
The Vampire turns into a bat, jumps on your head and starts to drain your health. You can stop this by standing in the giant areas of floor covered in candles.

Fury
The Vampire hits you five times taking a heart each time, the last hit sets you on fire.

Demonic minions
When the Vampire gets to a quarter of it's health it will spawn 4 Zombie Guardians to help kill you.

Rewards
In the coffin are 2 levers which open the doors of the castle and city.

When the Vampire dies it drops:

Hammer and Stake-Helps to deal with any other Vampires you find

Fire ring-Lets you breathe fire if you right click with it in your hand, and gives your punches fire damage if you left click with it in your hand

Vampires sword-One hits Zombies, Skeletons, Spiders, Creepers, Passive mobs and Zombie Pigmen

Also some of the houses have chests in them if you can be bothered to look.