Free/cheap Tileable 3D Assets

Hi people,

I know there have been some similar questions on here. I want to get started building some levels, but I don't know how to create 3D assets. I'm aware that there are various free 3D assets available, but many are one-off non-interactive meshes that aren't very suitable for what I want to do. Is anyone aware of things like road segments, sewer segments, wall segments, doorways etc which could be clipped together easily? A lot of the buildings I've seen are a solid mesh with no way to get inside. I'm fine with constructing the interior myself, but that's obviously hard if there are no entrances.

One that I saw (sewer segments) looked promising, but the reviews mentioned no L shaped pieces, so very limited utility for these.