This past week I continued the greybox level design. I got to the final stages of my greyboxing, where all I need to finish is the boss room, and then I'll move on to iterate on the layout and enemy positioning.
I had fun making a very large hall with columns, made a bridge, put a last tower with stairs where it takes you back to the beginning of the level (and to the boss area), and place the usual lights to guide the player.
Also in Unreal Engine thanks to Lumen is very convenient to be able to see the bounce of lights in dark areas right away, without having to do the usual slow bake lighting of static lights.
I also had to move a whole portion of the level to get the last tower to be near a particular area, but the fact that each room is a Group actor (each room is a group of walls, floors, lights and props), moving each room is like moving Lego blocks, it's very modular, and it took me just 5 minutes.