What's the easiest way to make curved 90 degree walls?

I am working on a level that has a lot of curved walls, I mosty want to use 90 degree curved walls, so they don’t have an edge. What’s the easiest way to do that in UE4? I put in some curved stairs for example and want to have walls around them so the player can walk between them to reach the top.

Actually, bsp shouldnt be used for final products.
its meant to be used as a blocking out tool, and later be replaced with static meshes made in an external 3d program like blender (free) or 3dsmax, maya, zbrush, modo, etc.

So even though Steve’s reply is correct, I highly suggest to not use bsp for this. (EVER)

Here is a way to do it with BSP Brushes, however the annoying thing at the moment is that you cannot soften the normals of the edges in engine afaik and it’s super inefficient. It would be a much better idea to make it in a modelling program.

Anyways here is what i got:

So first i created a cylinder BSP and changed the settings as shown (more edges and hollowness)

Then I created a box BSP, changed it to be Subtractive and large enough to cover half of the cylinder.

I then duplicated that box and positioned it so only a quarter of the cylinder is now showing.

You can now leave it this way and Duplicate those BSP’s to use as corners elsewhere. OR you can select all 3 BSP’s made and use the Create Static Mesh tool to convert it to a 3D model and save it in your asset folder.