Mountain Castle

The Mountain Castle, otheriwse known as Castle of Secrets, is a Snow Castle structure from the Better Dungeons mod. It is always a tall spire in a snowy biome, usually a glacier biome. At the bottom and outside of the castle is usually a vanilla village.

The Keep

There is an opening in the main gate that can be closed right inside the gatehouse in the left courtyard. Walker Archers will begin attacking from the battlements as soon as you approach the castle. Once you are inside, there are several places to explore before heading up in either direction.

The Village

Straight through all of the guards on the ground level, you'll find a village in the back through a shadowy path between rock overhangs. A skull on the ground marks a significant place. Gather all the loot here and go back to the courtyard.

Guard's Quarters

Now procede to work your way up the left staircase through the guard tower to approach the apartments on the hill. Loot those rooms, paying close attention to the topmost room in the courtyard. That's a big bookshelf, isn't it?

Off to the right is a bridge going into the mountain where the officers keep warm. Loot this area as well.

Stairway to ...

Head back to the entry courtyard to find a narrow winding stair up the mountain itself. It will be guarded and you may be knocked off of the path. Wear your cloud boots if you have them.

The Royal Apartments

At the top of the mountain is the real city where the royals live. There is a lot of loot and there are a lot of Diamond-Armored Walkers. The final secret is here. There is also a secret not mentioned in the mysterious book.

Boss

At the bottom of some of these structures, underneath, is a spider boss. Sometimes the worldgen doesn't place his lair well and it's gone by the time someone finds it. The Boss Spider drops its signature spider hook.