How do I use something similar to Landscapes to smoothly connect my floor and ceiling?

I’m looking to create a cave type scene, and it seems this has probably the least amount of tutorials for anything within unreal, and those demonstrations out there are just for nice renders, using about a thousand different meshes bundled together.

I’d like to be able to make one continuous shape connecting my ceiling and floor with no obvious seams, while also not using a thousand different meshes all with their own collision.

Is there any way to do this with unreal? I’ve seen this tutorial and I can’t help but think that there must be a better way.

Thank you for all advice.