What is the hallowed tower for on Pokemon diamond?

It is a place to catch the rare Pokemon Spiritomb. It is quite easy, but you must have a friend to help you get it.

1. You must go Underground with the stone in the Hallowed Tower and talk with a friend.
2. Go inside a Secret Base or leave the Underground then go back and talk to your friedn again. Re-peat this until you have spoke to your friend 33 times. (Check on your Trainer Card)
3. Click A whilst facing the Hallowed Tower and you should be battling Spiritomb. If not, feel free to contact me on my message board.