While thinking back on instance5 earlier today, I was reminded of how poor of a way it was to extend the Roundhouse system.
In a flash of inspiration, I was struck with the idea that you could add doorways, and then passages up or down, and those would fit perfectly with larger, outer rings of Roundhouse-style instances.
Immediately, I set to work prototyping this idea.

The current system supports up to 3 rings of instanced buildings.
The geometry between the rings can actually be pretty complex if you need it to be.
The instances are not perfectly assembled and some use-cases will leave nodraw gaps - one is even visible in the example VMF!

These instances also aren't nearly as detailed as my instance4 ones, and there aren't quite as many either.
My hope is that this system will be easier to understand than the other two sets of instances I've uploaded today, and people (or maybe just me) will be naturally inclined to edit them and add new features.

One idea that I think would be really sick would be to use the Greek Pack assets to create a modular set of instances that could be used to create colosseums and the like.
If ever I update this download, it'll be to add that.