Where do I implement methods only need in a level?

Hi!

I’m using Unreal 5.3.2 and I have a question about software design.

I have some methods that I only need them in a level (I use them to do some calculations). Where do I implement them? In a C++ class? In an Actor class? In a Game Subsystem? I don’t need to put them in a level, but I will call it from Blueprint and C++.

Thanks!