on route 208 (on the way to Hearthome city ) there is a person in hiding wedged in the corner of trees direct from the honey tree is. This person looks like a blackbelt trainer. he will give you an odd keystone this is a key which will let you fix the stone tower on route 209 (where the lost tower is ) you will be able to access this route when you progress through hearthome city and get the egg from the hiker (you will only get this egg if you've only reached hearthome city for the first time) once you are in route 208 go to the peculiar wrecked stone pillar at the corner that connects soleaceon and route 208 press the A button and it will ask you if you want to insert the keystone you obtained say 'yes' and it will become the 'hallowed tower'. Once this is done go and talk to at least 32 people underground (excluding the hikers) but dont worry you can talk to the same person and go out 32 times this will count as a different person each time. but be aware that this '''will''' take a while to do.
Now that all of the above is done go to the hallowed tower again and spiritomb will be there it will appear as level 25 so be sure to save before you go into battle with it as you may knock it out. Spiritomb is a GHOST/DARK type so bear that in mind when you use your moves against it as no moves are super effective against it. This pokemon is worth having as it can learn some very good moves (e.g: shadow ball and dark pulse) the champion of sinnoh has a spiritomb that is level 61 and it knows dark pulse, silver wind, shadow ball and ominious wind.
spiritomb- forbidden pokemon.
'''diamond-''' a pokemon that is made of 108 spirits it is bound to a fissure inside the odd keystone
'''pearl- '''it was bound to a fissure in the keystone for its misdeeds 500 years ago