Floor 1
Enter the castle using the combat menu. Immediately, a cutscene plays unlocking the castle. The first key to the first door is right in front of the first lock. Pick it up and continue on.
The next room has three interesting features: a locked door, a pressure plate, and a path with the following riddle: "There's a magical force that stops you from going here when it's not raining." To continue, use a Rain Healing Potion and click the arrow to the left. In this room is stranger tree (related to the achievement in elite woodcutting: Chop the tree from the castle (Floor 1)). In the middle of the room is also a key, to the previously mentioned locked door.
The next room has two interesting features: another locked door, and the Castle Ants. Killing them gives you the key to the door.
Castle Golem -- drops the stone needed for the button (can't remember where the button is off hand)
"There's a magical force that stops you from going here when it's not raining." -- use a rain potion
RGB puzzle -- ????
Arrows -- solution to floor 2 puzzle
Altar thing -- unlocks Purple Key Guardian
Floor 2 portal located just before the prison cells
Floor 2
Requires portal base 2 and portal 2 -- portal base 2 from elite gathering, portal 2 from g3
Arrow puzzle -- solution is arrows from floor 1
Secret room
Castle Merchant -- Sells g3 portal
Buying portal 3 from Castle Merchant -- requires purchasing the boots and attaching puffer needles to them to cross the ice. The hint is on a paper on the wall at the end
Door puzzle -- find the odd one out each time
**Note there is nothing past the goblin dad
Floor 3 portal located next to goblin dad across the ice
Floor 3
Requires portal base 3 and portal 3 -- portal base 3 from elite gathering, portal 3 from Castle Merchant
Arrow puzzle -- reverse order of the floor 1 arrows
Faradox fight -- required to start a quest. Attempt the fight.
Should obtain a new mould -- give all the metals it asks for. Drop it down the hole located near the beginning of floor 3. This unlocks the dungeon.
Dungeon
Currently only one room -- unlocks the Guardian Trio. These drop Guardian Combo Loot, which give G4 keys.