Do you need a game? or do you just want some tool to develop a 3d world?
Tools, you have sketchup, very simple, but maybe not what you are looking for.
Blender is by far the best tool for 3D development (free and open source), but it takes time to learn how to use it (you have a mode to draw directly in 3D)
If you are looking to make a game, Godot, unity3D, or gamemaker (pay only).
I would tell you to try Godot, it is open source, free and very light, so you have nothing to lose by trying and seeing if it suits you.
On the Internet you find many other options, but these have many tutorials, which makes it easy for you to learn how to use them.