If you enter through the main entrance, take note of the pedestal and the four suits of armor in the room. If you battled in the main courtyard, you’ll find an etched gem. Place that on the pedestal and have the Helm Guardians fight for you. Of course, if you’re after the experience points, take out the guardians too.
At the Helm’s Hold, you’ll find an altar room with a demon waiting for you. Chaohinon of the Void is a demon summoned by the False Helmites sent to crush the spirit guardian of Helm’s Hold. Unfortunately, his summoning was never finished and now this demon wants to be set free. There is a Black Grimoire in the room by the altar. Pick it up, if you’re into setting the demon free, if not keep it to use to banish the Demon – keep walking to the stairs going up, there is a room there and a Helmite waiting for you. Kill him and take the Ritual Book on the bookshelf before heading back to the ritual room. Now you have an option to complete the ritual or banish the demon. I suggest you banish the demon because restoring the Guardian of the Helm gives you a prize. However, both actions entail a reward of sorts, here’s the rundown for the rewards: For the Demon, you’ll get to pick from cloaks, double axes or a temporary buff. The Guardian of Helm will also give you a reward, between a magical item, weapons, a temporary buff or insights into the future.