There are many novices who don’t know how to open Niflheim in God of War 4, so the editor has brought the opening strategy of Niflheim in God of War 4. Friends who are interested can learn about it with the editor.
Like Muspelheim, Niflheim needs to collect the corresponding four rune fragments to open it.
The four rune fragments are located in the mask platinum treasure chests at the top of the mountain, the watchtower (the second water level drops), the ancient wight ruins, and the forgotten cave.

It is worth noting that when going to collect the rune fragments on the top of the mountain, you must use the Blade of Chaos to open the way. Therefore, it is impossible to open Niflheim before the main plot advances to Kratos picking up the Blade of Chaos.
God of War 4 system requirements
Minimum configuration:
Requires 64-bit processor and operating system
Operating system: Windows 10 64-bit
Processor: Coming Soon
Graphics Card: Coming Soon
DirectX version: 11
Storage space: 80 GB available space required
The above is all the information on how to open Niflheim in God of War 4. Interested friends, please come and watch!