See the previous post for direct walkthroughs to all stairways on the 1st and 2nd floors of the Snow Ruins. This post contains a walkthrough for the three main destinations on the 3rd Floor.
Direct Path to the Rune Storage Chamber and Shortcut Stairway
The third floor is different from the first two in that you now often will find platforms along the walls of the various chambers.
If you wish to go directly to the Rune Storage Chamber, ignore the platform in the first chamber.
From the first isolated stairway that leads to the 3rd floor, you need to find your way to the doorway where the Rune Storage Chamber is located. This is the ‘secret’ of the Snow Ruins and is the place where you will face Gelwein for the first time.
When you descend the isolated stairway to the third floor, you will find yourself in a small chamber containing two rocks that can be smashed for ores/gems. An ice barrier in the north prevents access to any other area.
Destroy the ice barrier and go north into a chamber that contains a single Generator that spawns Unicos and Demons as well as an Eye Generator.
Destroy the Eye Generator in this chamber to create an explosion that melts the ice on the sliding door in the east. Go east through a narrow corridor through another sliding door into a small chamber containing a swiveling cannon. Destroy its arch to destroy the cannon.
Unlocking the Shortcut Stairway
You will see two exits from this chamber. One is on the eastern wall and one is on the southern wall. Take the exit in the south first to open the sliding door to the shortcut stairway. Now return to the chamber in the north that held the cannon and take the exit in the east.
Path to the Rune Storage Chamber
You will find yourself in a little area with exits to the north and east. Go north into an ice chamber with a platform in the west and a swiveling cannon in the main area. The arch that controls the cannon is on the platform with a single monster generator that spawns 4 Demons.
If you continue north, you will find a ramp in the east that leads upward to another platform. Directly north, however, is a huge Minotaur encased in ice. Break the ice and destroy the Minotaur at one blow with a fire Axe and you will find yourself in front of the door to the Rune Storage Chamber.
Provided you encountered Gelwein previously in front of the Tower of Rest at Whale Island, you will experience an Event when you attempt to access the locked door to the Rune Storage Chamber.
Note that, when you have bested Gelwein here, a Circle Portal will appear leading directly to the entrance of the Snow Ruins. Whenever you use the Circle Portal, you will find yourself to the north of the ice-encased Minotaur.
Path to the 4th Floor Stairway
From the Circle Portal on the 3rd Floor and Rune Storage Chamber, go south to the little T-junction. If you are in the ice chamber that contained the ice-encased Minotaur, you will be at the ‘leg’ or lowest point of the T. You therefore will see a path that leads both east and west. If you go west, you will find yourself in the little chamber with the swiveling Cannon that leads to the shortcut stairway.
Go east instead if you wish to access the fourth floor for the first time.
You will find yourself at the southwest corner of an ice chamber with a platform to the east that is accessed by means of an ice ramp. The platform acts as a barrier to the eastern half of the ice chamber.
Asccend it to find an Eye Generator and a Treasure Chest. You will not find the arch for this Generator on the platform. Another ramp in the southeast leads downward to take you to the eastern half of this ice chamber.
The only other exit is in the northeast. Go through it to find yourself in a narrow chamber with two Monster Generators. The one in the north spawns a Mamoo and a Demon. Two rocks that can be smashed for ores/gems are in the middle of the chamber. Below it, to the south, is another Monster Generator that spawns two Demons and a Mamoo. You need not activate the southern Generator if you are bound for the 4th Floor.
If you go north from this chamber along a narrow corridor, you will find the isolated stairway to the 4th floor.