Landscapes are useful for large, outdoors spaces. Sounds like you mostly want to be indoors, in which case you don’t need a landscape.
“dynamic meshes” seems like a bad idea; they are much less optimized than static meshes, and especially than instanced static meshes. “don’t fill my content folder up too much” is a really bad reason to go with a very expensive runtime system.
Most indoor games use a combination of simple, modular assets (walls, doors, floors, ceilings, pillars and trim in certain styles) that are used everywhere, and specific decorative meshes that are used rarely, to break up the monotony.
You can also use the BSP system (“carving”) if you really want to, it’s not too inefficient (better than dynamic meshes, at least,) and very easy to cut rooms and corridors out of a very big cube. It is, however, quite hard to make high-poly content this way; you’ll typically want to build with trim meshes to make it less blocky.