Effects of Power
Now that you know the location of a place of power let us figure out the effects. Generally, the impact should be beneficial even though the areas may seem suitable for a negative impact. Positive impacts are seen in a more, well, positive light with players. But going back to a suitable negative location picture a graveyard. A graveyard seems like an excellent place for an effect that hurts players, and while that is true, it can be positive that hurt players. For example, instead of giving a penalty to saves against undead attacks against your players, you can provide a bonus to necromancy spells. This bonus is excellent when attacking with a vampire or lich but also useful when your players have cast necromancy spells.
Types of Power
So we know where the place of power is located and that it needs to be a buff. The next question is what you buff. This can be anything you want, from skills to damage to spells. Your imagination is your limit. You can do something special. For example, let’s keep going with the graveyard theme. Instead of giving necromancy spells advantage to attack or damage, you could lower the casting time of necromancy spells. On the other hand, you could double the duration of all necromancy spells.
While it may be tempting to just keep giving advantage when in places of power beware that it will get boring. One thing you can do is try auto passing or maxing the rolls. For example, a paladin fighting on the holy ground of their church gets max damage to all smite damage while both them and the enemy is there. Sometimes flat bonuses with no rolls can be exciting because the players know that they can accomplish things at this moment that they cannot normally do.
Story of Power
The place is a graveyard that gives everyone inside a reduction in casting time for all necromancy spells. This makes all spells that cost an action to be a bonus and spells that take longer than an action to be an action. This is an exciting location for players to encounter, not to mention the increasing power of necromancy spells. The next step is to create a story behind it.
A story behind a place of power gives it meaning, and some understanding of what is going on there, not to mention, can be a fun story point. The story can be virtually anything. In the graveyard, there could be a lone tombstone covered in shiny black stone. Or it could be the mass graveyard where the souls still curse their death. The story can be something the players learn to understand while they are there. Then again, it could remain a mystery.
Emphasis of Power
You have a story as to why things are happening there; however, it does not end there. The last part is the emphasis on the effect. This occurs when the power is used and is the final piece when creating a place of power. When the power is used, give a few words as to what is happening. The shiny black tombstone can radiate magical darkness that expands when the spell is cast. Or the souls give an audible moan whenever a necromancy spell is cast with visible pieces of soul erupting from the ground.